Mitsubishi HC-UF43K (HCUF43K) — MELSERVO HC Series 400W AC Servo Motor, Keyed Shaft, Flat-Type, IP65

What You're Getting

Part Number: HC-UF43K / HC-UFS43K (HCUF43K) Series: Mitsubishi MELSERVO-J2S — HC-UF Series Classification: Low Inertia, Small-Medium Capacity AC Brushless Servo Motor — Flat Type

The Short Version

If you run FANUC- or MELSERVO-era machine tools, robotics cells, or general-purpose motion systems from the late J2S generation, the Mitsubishi HC-UF43K is likely already a familiar number. It's a 400W brushless AC servo motor in Mitsubishi's flat-profile HC-UF family — compact enough to fit where space is tight, capable enough to handle precision feed axis duties, and equipped with a 17-bit absolute encoder that keeps the machine knowing where it is without a homing cycle every time the power comes on.

The "K" in the model designation means keyed shaft — there's a machined keyway for positive coupling torque transmission. No brake is built into this variant, so it's intended for horizontal axis applications or positions where axis load does not require positional holding at rest.

Technical Specifications

The Flat-Type Structure — Why It Matters

Mitsubishi engineered the HC-UF series with a distinctly shallow axial depth compared to conventional cylindrical servo motors of equivalent output. That flat body isn't just cosmetic — it's a practical dimension that opens up installation options in confined machine tool enclosures where a standard-length motor simply won't clear an adjacent casting, ball screw nut, or structural member.

The 122mm overall depth (shaft-through length excluded) gives machine builders a usable envelope that the HC-KFS and HC-MFS cylindrical series motors of the same 400W class cannot match in tight installations. On small vertical machining centres, horizontal tapping machines, and multi-axis transfer equipment where every millimetre of envelope counts, the HC-UF's profile has made it a persistent design choice for OEMs building compact precision machinery.

The 17-Bit Absolute Encoder — A Practical Explanation

The encoder fitted to the HC-UF43K is a 17-bit absolute serial pulsecoder, equivalent to 131,072 counts per shaft revolution. Two things matter here in practice.

Resolution. At 3,000 rpm driving a 10mm pitch ball screw through a 1:1 coupling, the control system's position resolution per encoder count works out to roughly 0.076 micrometres. That kind of granularity is what enables the J2S servo system's tight positioning repeatability and smooth low-speed following error performance in contouring applications.

Absolute retention. The encoder type is absolute, not incremental. Position data is retained across power cycles through the battery backup system in the MR-J2S amplifier — a CR2032 battery in the amplifier's battery holder maintains the counter memory when control power is off. When the machine restarts, every axis knows exactly where it is. No reference-return sequence, no homing cycle, no production delay. In high-volume manufacturing environments, this translates directly into cycle time and reduces operator interaction at every shift start or power restoration event.

Should the amplifier battery discharge fully or be removed while the motor is powered off, the absolute position data is lost and the machine will require a manual reference-point re-establishment before returning to normal automatic operation. The amplifier will display a battery warning alarm before voltage drops to the critical level — routine battery replacement on a two to three year cycle prevents this scenario.

Compatible Servo Amplifiers (MR-J2S Series)

The HC-UF43K is rated for use with the MR-J2S 40A-class amplifiers in all interface variants:

The amplifier-motor pairing is fixed by current class and motor series. Do not substitute a higher or lower current class amplifier without verifying the motor ID parameter table — an incorrect motor ID setting in parameter 0 will cause the servo to run with incorrect gain and current limit settings, which can produce instability or parameter alarm faults even if the motor appears to run at low speed.

Axis Applications This Motor Is Built For

CNC machine tool feed axes — X, Y, Z on small-format machining centres. The 400W output and 4,500 rpm maximum speed cover the full range of feed rates typical on small vertical and horizontal machining centres with moderate table loads and short axis travels. The flat body fits the compact enclosures these machines often use around the ball screw-motor interface.

Auxiliary positioning axes. Rotary index tables, automatic tool changer positioning drives, pallet shuttle actuators, and similar periodic-duty axes are a natural fit. The absolute encoder eliminates the need for a dedicated homing sequence on these axes, simplifying the PLC logic and reducing cycle time at workpiece changeover.

Assembly automation and robotic end-of-arm tooling. Where a compact, high-resolution positioning axis is needed without the added bulk of a gear-motor combination, the HC-UF43K provides direct positioning capability in a small package that integrates cleanly into MELSERVO J2S-based motion systems.

Semiconductor and electronic manufacturing equipment. The low rotor inertia (0.365 × 10⁻⁴ kg·m²) supports fast settling after point-to-point moves — a characteristic that matters in high-cycle-rate equipment where dwell time at position must be minimised to sustain throughput.

In-Stock, New Units — What to Know Before You Order

The HC-UF43K / HC-UFS43K is a discontinued Mitsubishi part. Mitsubishi Electric has not manufactured new units in this series for some time, having transitioned the J2S platform customers toward the MR-J4 and MR-JE series with the corresponding HG-series servo motors. The units currently available in the market are new old stock from legitimate supply channels — genuine Mitsubishi Electric product, manufactured in Japan, in original factory packaging.

Two things follow from this. First, verified new stock is genuinely new — not refurbished, not repaired — and carries the same performance and reliability as it would have on original supply. Second, stock is finite. Once the current legitimate inventory in the global supply chain is consumed, new OEM units will no longer be available and any remaining procurement will be limited to refurbished or repaired units. For users maintaining a fleet of J2S-era machines, stocking a forward supply of critical servo motors now is straightforward insurance against unplanned downtime when lead times on refurbished units could extend to weeks.

Handling and Storage Notes

The HC-UF43K is a precision device. A few practical points:

When mounting, do not use a rigid coupling between the motor shaft and ball screw without verifying shaft run-out. Mitsubishi specifies the run-out of the ball screw shaft at the coupling interface should be kept to 0.01mm or less — misalignment at this junction generates periodic radial load on the motor's front bearing that shortens bearing service life and can introduce cyclic noise on the encoder signal.

Install the motor with the power cable and encoder cable oriented downward where possible, or provide a drip loop in the cables before they reach the connector. This prevents fluid from tracking along the cable jacket into the connector body. The IP65 rating covers the motor housing; it depends on correct connector seating and cable routing to be fully effective in wet environments.

Never strike the shaft or encoder housing during coupling installation. The encoder is an optical precision assembly mounted directly behind the rear bearing; any shock transmitted to the encoder disc or PCB can cause damage that may not be immediately apparent in a brief functional check but will manifest as position error or alarm faults under load.

HC-UF Series Variant Reference

All variants share the same 400W output, 1.3Nm rated torque, 3,000rpm rated speed, 17-bit encoder, and 80×80mm flange.

FAQ

Q1: What is the difference between the HC-UF43K and the HC-UFS43K, and will either work as a direct replacement for the other in my machine?

The HC-UF43K and HC-UFS43K are functionally the same motor. The "UF" and "UFS" designations both refer to the flat-type (slim-profile) motor within Mitsubishi's HC series; the "S" in HC-UFS is sometimes used to indicate the specific slim body structure. Both carry the same 400W output, 1.3Nm rated torque, 3,000rpm rated speed, 17-bit absolute encoder, keyed straight shaft, and 80×80mm flange dimensions. In field service practice, these two part numbers are treated as direct substitutes. If your machine's documentation or axis motor label shows HC-UF43K and you are sourcing HC-UFS43K stock (or vice versa), the unit will fit mechanically, connect electrically with the same cables, and operate correctly with no parameter changes required.

Q2: My machine uses an MR-J2S-40A amplifier. After replacing the HC-UF43K motor, the axis moves erratically and generates a following error alarm. What should be checked first?

The most common cause of this specific symptom after a motor swap is an incorrect motor ID setting in the servo amplifier parameters. On the MR-J2S-A series, parameter No. 0 (motor selection) must be set to the value corresponding to the HC-UF43 / HC-UFS43 motor model. If the parameter was not cleared or reset during the replacement, the amplifier may still be configured for the previous motor type. Perform a servo parameter initialisation from the amplifier's parameter unit or via MR Configurator software, select the correct motor model, then save and power-cycle the system. Also verify that the U/V/W power leads and encoder cable are fully seated with no bent pins. A loose encoder connector produces erratic position feedback that presents identically to a gain-related following error at the control level.

Q3: The HC-UF43K is listed as discontinued. Is a new unit still a genuine Mitsubishi Electric product, and what does that mean for warranty and longevity?

New-old-stock units of the HC-UF43K are genuine Mitsubishi Electric products manufactured in Japan to the original specification. Being discontinued means Mitsubishi is no longer producing new units, but it does not mean existing new inventory is in any way inferior to production-current stock. A genuine new unit in original packaging will perform to its full rated specification and can be expected to provide the same service life as any new servo motor, provided it is correctly installed and operated within its environmental and load ratings. Legitimate distributors offering new HC-UF43K stock are selling from verified supply chain inventory, not reconditioned units. When evaluating a purchase, look for original Mitsubishi Electric packaging and a verifiable source. What discontinued status does mean practically is that supply is non-replenishable — once global new stock is exhausted, only refurbished units will be available, typically at higher cost and with longer lead times.

Q4: Can the HC-UF43K be used with a newer MR-J4 series amplifier, or is it locked to MR-J2S?

The HC-UF43K is not natively compatible with MR-J4 amplifiers and cannot be directly connected to one. The MR-J4 series is designed for the HG-series servo motors with a different encoder protocol and connector interface. There is a migration path available through Mitsubishi's conversion hardware (specifically the MR-J4-B-RJ020 and MR-J4-T20 combination for SSCNET-based systems), which allows an MR-J4 amplifier to operate within an existing MR-J2S-B SSCNET-based motion controller system — but this still drives HG-series motors, not the HC series. For machines that must remain on HC-UF43K motors, the MR-J2S amplifier series remains the correct drive platform. If a full drive upgrade is being planned, the standard Mitsubishi migration path is to replace both the amplifier and motor together: MR-J4 amplifier paired with the corresponding HG-KR or HG-SR series motor in the equivalent torque class.

Q5: Are there any specific storage requirements for new HC-UF43K units being held as maintenance spares, and how long can they be stored before the encoder needs to be verified?

Store new units indoors in the original packaging, in a dry location between 0°C and +40°C (operating range) or up to +70°C for short-term storage. The two practical concerns for long-term storage of servo motors are bearing grease migration and the optical encoder assembly. Bearing grease can settle over extended static periods, which can cause a temporary increase in friction after long storage that normalises within a few rotations. To manage this, the shaft should be turned by hand through several revolutions every three to six months during storage. The encoder assembly in the HC-UF series is a sealed optical unit that does not require maintenance in storage, but units that have been stored for more than two years should have a functional encoder verification test — confirming that the A, B, and Z-phase signals are clean and within specification — before being installed in a machine. This is standard practice for any precision encoder that has been in static storage, and avoids the scenario of discovering a storage-related encoder issue after the motor is already mounted in a machine.