Mitsubishi HC-SFS301B AC Servo Motor — 3 kW / 1,000 rpm | 28.6 Nm | Electromagnetic Brake | MELSERVO J2S | New In Box

Not every servo application calls for high speed. There is an entire category of machine tool axes, rotary tables, and industrial robot joints where what matters above all else is torque at low speed — the ability to hold and drive substantial loads with precision, and to lock the shaft securely when the machine is powered down. The Mitsubishi HC-SFS301B is built for exactly that requirement: a 3 kW medium-inertia motor delivering 28.6 Nm rated torque at 1,000 rpm, fitted with a factory-installed electromagnetic brake and Mitsubishi's 17-bit absolute encoder. New in original sealed packaging, available for fast shipping.

Technical Specifications

1,000 rpm, 28.6 Nm — Torque-Optimized Performance

The HC-SFS301B occupies a specific and well-defined performance niche. The HC-SFS series offers the same 3.5 kW frame size in a 2,000 rpm variant (HC-SFS352) and a 3,000 rpm variant (HC-SFS353) — both prioritize higher speed at lower torque. The HC-SFS301 works the opposite end of that trade-off: rated at 1,000 rpm with a 28.6 Nm continuous torque, it delivers more than twice the rated torque of the 2,000 rpm variants at equivalent power.

What does this mean in practice? At 1,000 rpm with 28.6 Nm, this motor is operating at its strongest continuous point, generating 3 kW of useful mechanical power through sustained, high-force, low-speed motion. The peak torque of 85.8 Nm (three times rated) provides the transient acceleration authority to drive heavy loads through sharp motion transitions without exceeding thermal limits in steady operation.

This torque-speed profile maps directly onto the requirements of large rotary table drives, heavy-fixture 4th and 5th axis motion, robotic shoulder joints, and any axis where the load mass or friction makes low-speed torque the dominant design constraint.

Electromagnetic Brake — The B That Changes Everything

The B suffix designates the spring-applied electromagnetic brake integrated into this motor. Understanding how it works explains why it matters:

The brake is power-off type — the spring locks the shaft when brake coil voltage is absent, and releases when 24V DC is applied. This is the fail-safe configuration. Loss of power, emergency stop, guard door opening, or intentional machine shutdown: in all cases, the shaft locks immediately without any command from the control system. Restoring power releases the brake and allows normal servo operation to resume.

For a motor rated at 28.6 Nm continuous torque and capable of 85.8 Nm peak — driving a rotary table, a tilting head, or a robot arm under significant gravity loading — the mechanical holding function of the brake is not optional. Without it, a powered-down vertical or inclined axis would descend under load. With the HC-SFS301B, the shaft stays exactly where it was when power is removed.

The electromagnetic brake is a mechanical holding device, not a dynamic braking element. It engages after the axis reaches rest, providing static holding force independent of servo current. Mitsubishi's guidance is to keep vertical axis unbalanced load torque within 70% of motor rated torque for reliable brake holding across temperature and wear.

Oil Seal and IP65 — Sealed for the Shop Floor

The drive-end shaft of the HC-SFS301B passes through a factory-fitted oil seal, closing the primary contamination path into the bearing and encoder cavity. On machine tools and production equipment where cutting fluid, coolant mist, and metallic particulate are present in the environment, the oil seal is what prevents those contaminants from degrading the bearings and encoder over thousands of operating hours.

The IP65 motor housing provides complete dust exclusion and resistance to water jets from any direction. The combination of oil seal and IP65 enclosure makes this motor suitable for direct installation on machine tools without additional protective enclosure — the standard requirement for a 3 kW servo motor in a CNC environment.

17-Bit Absolute Encoder — 131,072 ppr, No Homing at Startup

The encoder delivers 131,072 position counts per motor shaft revolution through Mitsubishi's high-speed serial link to the servo amplifier. Being absolute, it retains full position knowledge through power cycles — with the A6BAT battery installed in the amplifier, the multi-turn counter persists through machine shutdowns.

For a heavy rotary table or 4th axis drive where the reference return homing sequence takes a meaningful amount of time on each startup, eliminating that routine is a concrete production advantage. Every power cycle, every shift change, every scheduled maintenance stop — the machine is ready immediately without waiting for axes to home. Across a machine's service life, that operational efficiency adds up to substantial production time recovered.

Compatible Servo Amplifiers

The HC-SFS301B pairs with the MR-J2S-350A (analog/pulse-train command) or MR-J2S-350B (SSCNET digital network command) servo amplifiers, both rated at 3.5 kW in the MELSERVO J2S platform and confirmed compatible with the HC-SFS301 motor family.

The electromagnetic brake requires a separate 24V DC power supply wired to the brake connector per Mitsubishi's installation specifications. The servo amplifier does not supply brake power directly — a dedicated 24V source must be included in the machine electrical design.

Application Environments

The HC-SFS301B's torque-forward 1,000 rpm profile combined with the electromagnetic brake makes it the first-choice specification for a well-defined set of applications:

Large-format 4th and 5th axis rotary tables on CNC machining centers — the 28.6 Nm rated torque at 1,000 rpm provides the drive force for heavy workholding fixtures, the brake holds them safely during non-cutting segments, and the absolute encoder eliminates homing on every startup

CNC turning center cross slides and deep-hole drilling axes — applications where feedrate is moderate but cutting forces demand high sustained torque throughout the cut

Industrial robot shoulder joints — the primary axis on medium-payload industrial robots where the combination of 3 kW output, high torque, and mechanical holding brake is the standard joint specification

Automated welding and cutting positioner drives — headstock and tailstock rotation axes on positioners that hold large weldments require exactly the torque density and brake holding function this motor provides

Heavy automated material handling — pallet rotation, fixture tilting, and barrel indexing mechanisms in automated production cells where load mass makes high-torque, low-speed servo control the only viable approach

HC-SFS301 Variant Overview

The HC-SFS301 base motor is available in several mechanical configurations, all sharing the same 3 kW output, 17-bit absolute encoder, oil seal, IP65 housing, and 176 × 176 mm flange:

• HC-SFS301 — straight shaft, no brake
• HC-SFS301B — straight shaft, with electromagnetic brake (this listing)
• HC-SFS301BK — keyed shaft, with electromagnetic brake

The HC-SFS301B is correct for installations using a clamp coupling on a plain shaft where the brake is required. For driven components with a keyed bore, the HC-SFS301BK provides the same brake function with the keyed shaft interface.

FAQ

Q1: Which servo amplifier is compatible with the HC-SFS301B?

The HC-SFS301B pairs with the MR-J2S-350A (for analog or pulse-train command from a PLC or external CNC) or MR-J2S-350B (for SSCNET multi-axis network systems with Mitsubishi motion controllers). Both are rated at 3.5 kW within the MELSERVO J2S platform. The electromagnetic brake requires a separate 24V DC supply — it is not powered by the servo amplifier directly.

Q2: What power supply does the electromagnetic brake require, and how is it wired?

The brake coil requires a dedicated 24V DC power supply wired to the motor's brake cable connector. The brake releases (shaft free) when 24V DC is applied, and locks (shaft held) when voltage is removed. The 24V supply must be included in the machine electrical cabinet design independently from the servo amplifier supply. Wire size, connector type, and interlock logic requirements are specified in Mitsubishi's servo motor instruction manual for the HC-SFS series.

Q3: What is the difference between the HC-SFS301 and HC-SFS302 or HC-SFS303 models?

The three models represent different rated speed configurations of the HC-SFS 3kW family. The HC-SFS301 is the 1,000 rpm rated variant with the highest torque output (28.6 Nm). Higher-numbered variants operate at 2,000 rpm or 3,000 rpm with progressively lower rated torque. Select the 301 when high continuous torque at low-to-moderate output speed is the primary requirement; select higher-speed variants when the application demands faster axis movement at lower torque load.

Q4: Does the HC-SFS301B support absolute position retention through power-off cycles?

Yes. The 17-bit encoder is an absolute type. With a Mitsubishi A6BAT backup battery installed in the servo amplifier, multi-turn position data is preserved when the machine is shut down. At the next startup, all axis positions are immediately available without a reference return sequence. For machines with heavy fixture loads where homing would require careful manual management of brake and axis movement, this zero-homing startup is a meaningful operational benefit.

Q5: Is the HC-SFS301B still in production, and what is the current-generation equivalent?

The HC-SFS series belongs to Mitsubishi's MELSERVO J2S generation, which has been succeeded by J4 and J5 series products. New-in-box HC-SFS301B units remain available for machine maintenance and existing J2S-platform installations. Mitsubishi's current-generation equivalent in the 3 kW / 1,000 rpm class with brake is the HG-SR301B (MELSERVO J4 series) — offering a 22-bit encoder and IP67 housing, but requiring J4 amplifiers and different cable interfaces. For existing J2S machines, the HC-SFS301B is the directly compatible replacement.