Mitsubishi HC-SF301B (HCSF301B) — 3kW AC Servo Motor, Straight Shaft + Brake, 1000 rpm, MELSERVO J2 Series

Product Identification

Part Number: HC-SF301B

Also Searched As: HCSF301B, HC-SF-301B

Series: Mitsubishi MELSERVO HC-SF (J2 Generation)

Motor Type: AC Brushless Servo Motor — Straight Shaft with Electromagnetic Brake, 1000 rpm

Condition: New In Box, Factory Sealed

Overview

The Mitsubishi HC-SF301B sits in a specific corner of the MELSERVO servo lineup: 3kW of rated output at a relatively low rated speed of 1,000 rpm. That combination produces a continuous torque figure — 28.6 Nm — that is unusually high for a motor of this physical size. Where a higher-speed servo motor generates a given wattage through fast rotation with moderate torque, the HC-SF301B does it the other way: slower speed, considerably more torque available at the shaft without reduction gearing.

That characteristic makes this motor the right specification for a different kind of load than a typical 2000–3000 rpm machine tool axis motor handles. Directly coupled pallet drives, rotary table direct-drive applications where gearing has been eliminated, conveyor systems running at low shaft speeds, and any mechanism where the load torque remains close to the rated value throughout most of the duty cycle — these are environments where the 1000 rpm, high-torque profile of the HC-SF301B earns its specification.

The "B" in the part number is the electromagnetic brake — a spring-applied, fail-safe holding device that keeps the shaft stationary when 24V DC is removed. Paired with a straight shaft for friction-clamp coupling interfaces, this is the configuration for brake-equipped horizontal or vertical axes where the shaft interface does not require a keyway. The brake variant is essential for any axis that holds a load under gravity or must maintain position through power-off events, e-stops, and alarm conditions.

This motor belongs to the original HC-SF J2 generation, equipped with the platform's 14-bit serial absolute encoder. It is compatible with both the original MR-J2-350 amplifiers and the later MR-J2S-350 amplifiers, making it a fit for machines running either generation of Mitsubishi servo hardware.

Technical Specifications

The 1000 rpm Profile — Why Rated Speed Matters

Speed and torque are always in tension in a given frame size. A motor running at 2,000 rpm with 3kW output produces about 14.3 Nm continuously. Run the same power through a 1,000 rpm winding design, and the continuous torque figure rises to 28.6 Nm — exactly double. The physical envelope of the motor does not need to change; the electromagnetic design shifts the operating point.

This matters enormously when sizing a drive system. The load torque required to move a mechanism at steady state determines whether a given motor can do the job continuously or will overheat trying. On axes where the load torque is high relative to machine speed — heavy toolchangers cycling at moderate rates, pallet changers transferring large fixtures, winding drives handling dense coils — a 2,000 rpm motor at 3kW will run into its thermal ceiling far sooner than the HC-SF301B under the same mechanical demand.

The 85.9 Nm peak torque is equally relevant. At three times the rated continuous figure, the amplifier can call for maximum acceleration torque for short bursts — getting a high-inertia load up to speed and stopping it — without requiring the motor to sustain that current level. Properly sized against the load's inertia and duty cycle, the HC-SF301B operates well within its continuous rating during most of the working cycle, using the peak capacity only during the acceleration and deceleration phases of each motion.

Straight Shaft and Brake — This Configuration in Context

Straight shaft: The HC-SF301B uses a plain cylindrical shaft, sized to accept friction-clamp or split-clamp couplings. This is the standard interface for disc couplings, bellows couplings, and jaw couplings with split-clamp hubs where axial fit and clamping friction transmit the torque. At 28.6 Nm continuous and 85.9 Nm peak, the coupling selection and installation torque are not details to leave to guesswork. The hub bore must match the shaft diameter within appropriate tolerance, and the clamping fasteners must be torqued to the coupling manufacturer's specification for the peak torque value — not the rated continuous value — to ensure no slip occurs during demanding motion profiles.

For anyone transitioning between shaft configurations: the keyed variant of this motor is the HC-SF301BK, which adds a machined keyway to the shaft but is otherwise identical. The two are mechanically interchangeable at the flange mounting point; the only change is the coupling interface at the driven end.

Electromagnetic brake: At 3kW and 28.6 Nm continuous, the stakes of an unbraked axis losing power are proportional to the load it carries. A brake-equipped motor in a vertical or heavy horizontal application means the axis holds position the moment 24V DC is removed — whether by design during a controlled shutdown or by necessity during a fault condition. The spring-applied design is fail-safe by nature: it needs power to stay open, not to close.

As with all servo motors with electromagnetic brakes, the correct sequencing through the MR-J2 or MR-J2S amplifier's MBR (brake interlock) output is important. The amplifier decelerates the axis to rest before the brake is released to engage. Bypassing this sequencing — connecting the brake coil directly to an e-stop relay without the MBR interlock — risks engaging the spring against a still-moving shaft, which quickly degrades the brake friction surfaces and may cause mechanical shock in the load mechanism.

J2 Generation — Encoder and Amplifier Compatibility

The HC-SF series uses the 14-bit serial absolute encoder at 16,384 positions per revolution. This is the original J2-generation feedback device, and it is what distinguishes the HC-SF family from the later HC-SFS series, which upgraded to the 17-bit encoder at 131,072 ppr.

In practical terms, 14 bits is still a capable encoder for the applications the HC-SF301B is designed for. On a 1,000 rpm axis driving a load through reduction gearing, the effective resolution at the load — once the gear ratio multiplies the motor counts — is typically more than adequate for positioning and velocity control tasks. The difference between 14-bit and 17-bit becomes more apparent on direct-drive or high-ratio applications running at low speeds where every count of encoder resolution contributes to smooth velocity control.

The absolute function keeps working between power cycles, backed by the A6BAT battery housed in the servo amplifier. As long as that battery is healthy, the machine restores absolute position on the next power-up without a homing sequence.

Amplifier compatibility is broader for HC-SF motors than for HC-SFS motors. Because the HC-SF encoder predates the J2S platform, it is readable by:

• MR-J2-350A / MR-J2-350B — Original J2-generation amplifiers (analog/pulse and SSCNET variants)
• MR-J2S-350A / MR-J2S-350B / MR-J2S-350CP — J2-Super amplifiers, backward-compatible with the HC-SF encoder

The HC-SFS301B (the J2S equivalent with 17-bit encoder) requires MR-J2S amplifiers and will not work with the original MR-J2. The HC-SF301B has no such restriction — it runs on either amplifier generation. For maintenance teams supporting older machines with first-generation MR-J2 amplifiers, this matters: the HC-SF301B is the correct motor for that hardware without requiring an amplifier upgrade.

HC-SF vs HC-SFS — Knowing Which Motor Your Machine Needs

The two families look almost identical from the outside and share the same flange dimensions. The distinction is internal and wiring-related.

When sourcing a replacement, verify the amplifier generation currently installed. Connecting a 17-bit encoder motor to a first-generation MR-J2 amplifier will result in an encoder error alarm and the axis will not operate. If the amplifier is MR-J2 (without the "S"), source the HC-SF301B. If the amplifier is MR-J2S, either variant will work — though for a like-for-like swap, the HC-SF301B remains the exact match.

Typical Applications

Rotary table and trunnion drives. 4th-axis rotary tables that index at modest speed under the weight of a large workpiece and fixture need sustained holding torque when clamped and repeatable index positioning while rotating. The HC-SF301B's 28.6 Nm continuous rating handles substantial table inertia without the motor working at high duty, and the brake holds the rotary axis mechanically between cycles when clamping is insufficient alone.

Pallet transfer systems on horizontal machining centres. Pallet shuttles move heavy pallets between machining and loading positions at relatively low speeds but high torque demand. The 1,000 rpm rating and high continuous torque make the HC-SF301B well-suited to this duty, particularly in older-generation Mitsubishi HMC systems that originally specified MR-J2 amplifiers.

Chip conveyor and coolant circulation drives. Some larger-format machine tool auxiliary drives — chip conveyors, screw conveyors, and integrated coolant circulation systems — use servo drives where speed regulation and controlled starting are required. Low-speed, high-torque servo motors fit this role where a standard induction motor would require external gearing.

Winding and material handling axes. Roll-to-roll material handling systems, wire winding machines, and similar applications use 1,000 rpm servo drives in torque control mode to regulate web tension or winding torque directly without reduction gearing. The motor's torque at the shaft is the control variable, and the HC-SF301B's rated torque provides ample capacity for medium-capacity winding applications.

Clutch-driven press and stamping auxiliary axes. Mechanical press auxiliary servo axes — material feed units, part eject mechanisms — operate at low speeds and require precise control of feed distance per press cycle. The combination of high torque, absolute position retention, and brake hold covers the functional requirements of these axes accurately.

New In Box, Factory Sealed

The HC-SF301B offered here is original Mitsubishi packaging — factory-sealed carton, shaft and connector covers undisturbed, internal packing foam intact. New-in-box means the motor has never been powered, never installed, and carries no service history to account for.

For machines currently down waiting on this part, in-stock new-in-box eliminates the repair turnaround time variable entirely. For planned maintenance inventories, factory-sealed stock stores reliably for multiple years under correct conditions: cool, dry, vibration-free environment, away from direct light and humidity extremes. Beyond five years, periodic slow shaft rotation as part of a storage maintenance routine helps redistribute bearing grease before the motor is placed in service.

Frequently Asked Questions

Q1: Which amplifiers are compatible with the HC-SF301B?

The HC-SF301B works with both the original J2-generation and J2-Super amplifiers at the 350 class. Confirmed compatible models are the MR-J2-350A (general-purpose analog/pulse, J2), MR-J2-350B (SSCNET, J2), MR-J2S-350A (general-purpose, J2S), MR-J2S-350B (SSCNET, J2S), and MR-J2S-350CP (built-in positioning, J2S). The HC-SF's 14-bit encoder is readable by both generations. The motor is not compatible with MR-J3 or MR-J4 amplifiers, which use a different encoder interface entirely.

Q2: What is the difference between the HC-SF301B and the HC-SFS301B?

Both motors are 3kW, 1,000 rpm, straight shaft with brake, 176 × 176 mm flange — mechanically interchangeable at the mounting face. The critical difference is the encoder generation. The HC-SF301B uses a 14-bit encoder (16,384 ppr) and is compatible with MR-J2 and MR-J2S amplifiers. The HC-SFS301B uses a 17-bit encoder (131,072 ppr) and requires MR-J2S amplifiers — it will not run on first-generation MR-J2 hardware. Match the motor to the amplifier currently installed in the machine.

Q3: Why does a 3kW motor have such high rated torque (28.6 Nm)?

Torque and speed are related by power: P = T × ω. With the same 3kW output at 1,000 rpm instead of 2,000 rpm, the rated torque doubles compared to a 2,000 rpm motor of the same capacity. The HC-SF301B produces 28.6 Nm continuously precisely because it is designed for slower-speed, higher-torque applications where the load demands sustained torque rather than high shaft speed. For high-torque axes that would otherwise need reduction gearing, this can simplify the mechanical design.

Q4: How does the electromagnetic brake work, and is it safe to use as a stopping brake?

The brake is spring-applied and fail-safe — spring pressure engages the brake disc, and 24V DC releases it. The moment power is removed, the spring clamps the shaft. It is a holding device only, not a stopping brake. It must be allowed to engage only after the amplifier has decelerated the motor to rest, using the amplifier's MBR (brake interlock) output to sequence the brake relay correctly. Engaging the spring against a moving shaft at 3kW causes rapid brake wear and mechanical shock.

Q5: Can the HC-SF301B be replaced with a HC-SF302B if only the 302B is available?

Only partially. The HC-SF302B is 3kW at 2,000 rpm with approximately 14.3 Nm rated torque — the same output power but half the continuous torque and double the rated speed. If the load requires close to 28.6 Nm of continuous torque at low shaft speeds, the 302B will not handle that demand adequately and will overload. If the load is lightly torque-loaded and the axis simply needs 3kW at moderate speed, a 302B could be functional — but would require parameter changes (electronic gear ratio, speed limits, acceleration settings) and a review of the duty cycle against the 302B's torque limits. For a true like-for-like replacement, source the HC-SF301B.