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Mitsubishi HC-SFS353B (HCSFS353B) — 3.5kW AC Servo Motor with Electromagnetic Brake, Straight Shaft, 3000 rpm, MELSERVO J2-Super Series

Product Overview

Part Number: HC-SFS353B

Also Searched As: HCSFS353B, HC SFS 353B, HC-SFS-353B

Series: Mitsubishi MELSERVO HC-SFS (J2-Super Generation)

Classification: Medium-Inertia AC Brushless Servo Motor — 3.5 kW, 200V class, 3000 rpm, Straight Shaft, Spring-Applied Electromagnetic Brake

Two Facts That Define This Motor

Within the HC-SFS 3000 rpm family, the HC-SFS353B occupies a specific position that two characteristics define completely.

The first is its place in the capacity range. The HC-SFS353 is the top of the compact 3000 rpm family — the highest-output motor in the HC-SFS 3000 rpm range before the series steps down to a smaller flange at lower wattages. At 3.5kW, it steps up to the 176 × 176 mm flange, separating it physically from the 500W through 2kW 3000 rpm motors that all share the 130 × 130 mm frame. When 2kW is not quite enough torque for a 3000 rpm axis and the machine structure can accommodate the larger frame, this is where the selection lands.

The second is the brake. The "B" suffix means spring-applied, electrically released electromagnetic brake — the design where 24V DC holds the shaft free and the spring closes the brake the moment that voltage disappears. On a 3.5kW axis with 11.1 Nm rated torque and a vertical or inclined load, this is not optional equipment. It is the feature that makes the axis mechanically safe at rest, under E-stop, and during any power interruption.

Everything else — 17-bit absolute encoder at 131,072 ppr, IP65 protection, MR-J2S-350 amplifier, 33.3 Nm peak torque — is shared with the rest of the HC-SFS 3000 rpm family at this capacity.

Technical Specifications

3000 rpm at 3.5kW: The Speed Advantage at This Power Level

Most 3.5kW servo motors in industrial use run at 2,000 rpm. The HC-SFS353B runs at 3,000 rpm — and that difference in rated speed, at the same power output, has a direct mechanical consequence that defines where this motor belongs.

Power equals torque multiplied by angular velocity. Hold the power constant and raise the speed, and the torque must fall proportionally. At 3,000 rpm and 3.5kW, the HC-SFS353B delivers 11.1 Nm continuous torque. The comparable 2,000 rpm motor — the HC-SFS352B — delivers 16.7 Nm at the same power level.

That is a significant torque reduction. So why choose 3,000 rpm?

The answer is shaft speed. Mechanisms that need rotational speed to function efficiently — direct-coupled ball screws running at high traverse rates, primary drives on high-throughput conveyor and transfer systems, winding station drives covering wide diameter ranges, high-speed cutting machine feed axes — benefit from a motor that delivers that speed directly. A 10mm pitch ball screw coupled directly to the HC-SFS353B reaches 30 m/min linear speed at rated shaft speed. Achieving the same traverse speed from a 2,000 rpm motor would require either a 1.5:1 gear or belt stage between motor and screw — adding cost, mechanical complexity, backlash, and inertia to the axis.

For applications where 11.1 Nm continuous torque is adequate for the load requirement and shaft speed is the primary performance driver, the HC-SFS353B at 3,000 rpm solves the problem more cleanly than a 2,000 rpm motor with a reduction stage in front of it.

The 33.3 Nm peak — three times continuous — handles the acceleration transients. A rapid point-to-point positioning axis at this capacity and speed draws heavily on peak torque to ramp up and ramp down, then settles to a fraction of rated torque during constant-velocity motion. The MR-J2S-350 amplifier's electronic thermal model tracks this duty cycle and protects the motor against cumulative thermal overload under aggressive cycling.

The maximum speed of 4,500 rpm extends the operating range above the 3,000 rpm rated point in the constant-power region. Available torque decreases above rated speed, but for rapid traverse phases on light-load axes this extended range can reduce positioning time without operating outside the motor's design envelope.

The 176 × 176 mm Flange: Top of the Compact 3000 rpm Range

One of the HC-SFS353B's defining physical characteristics is the 176 × 176 mm flange — and it is worth being explicit about why this matters for machine design.

The HC-SFS 3000 rpm family from 500W through 2kW (HC-SFS53 through HC-SFS203) all share the 130 × 130 mm flange. The HC-SFS353B steps up to the 176 × 176 mm frame — the same mounting interface used by the entire HC-SFS 2000 rpm family from 2kW through 7kW.

This has two practical implications.

First, a machine designed around the 130 × 130 mm frame cannot directly accommodate the HC-SFS353B without modifying the motor mounting interface. If the axis was originally designed for an HC-SFS203B (2kW, 3000 rpm, 130 × 130 mm), stepping up to the HC-SFS353B requires a new motor mounting plate and potentially changes to adjacent structure. This is not an insurmountable problem, but it is a real design task that should be anticipated.

Second, the 176 × 176 mm flange shared with the 2000 rpm family means that a machine frame built for any HC-SFS motor at 2kW or above can accommodate the HC-SFS353B without modification. For a machine originally designed around HC-SFS202B, HC-SFS352B, or HC-SFS502B motors where a 3,000 rpm drive turns out to be the better fit for a specific axis, the HC-SFS353B drops in without structural change — just a motor and amplifier swap.

The Brake in Detail: Why Spring-Applied Is the Only Acceptable Design for Vertical Axes

At 3.5kW driving a vertical or inclined mechanism, the fail-safe characteristic of the spring-applied brake is not a specification detail — it is the engineering requirement that the brake exists to meet.

The core property: the coil must be continuously energised with 24V DC to keep the shaft free. Remove that voltage for any reason and the spring closes the brake immediately. The axis is held mechanically without any dependence on the amplifier being functional, servo lock being active, the PLC executing correctly, or any other active system continuing to operate.

Consider the events this covers on a production machine. E-stop from operator: 24V removed, brake closes. Amplifier fault causes servo trip: 24V may be removed via the safety circuit, brake closes. Unplanned mains interruption mid-production: panel power drops, 24V to coil drops, brake closes. Deliberate servo-off at end of cycle: sequenced coil de-energisation, brake closes and holds the axis for the next cycle start.

In every case, the spring does the work passively. There is no requirement for any electronic system to detect the fault and issue a brake command. The spring-applied design is fail-safe by mechanical construction, not by software logic.

For a 3.5kW axis with 11.1 Nm rated torque driving a gravity-loaded mechanism — a heavy Z-slide on a machining centre, a loaded gantry arm, a tilted rotary table, a servo-actuated press ram — this characteristic is what keeps the machine safe and the load stationary under every failure mode that can occur in a production environment.

Vertical axis torque guideline. Mitsubishi's documentation carries a consistent recommendation: on vertical axes with gravitational unbalance, keep the sustained gravitational torque component at 70% or below the motor's rated continuous torque. At 11.1 Nm rated, that ceiling is approximately 7.8 Nm of sustained gravitational load during motion. Axes approaching or exceeding that figure benefit from a mechanical counterbalance to reduce the continuous torque demand during motion. The spring-applied brake removes all gravitational torque demand entirely during standstill — but during the moving phases, the motor must carry the full gravitational load component within this 70% guideline.

Brake Wiring and Sequencing at This Power Level

The electromagnetic brake on the HC-SFS353B requires a dedicated 24V DC circuit in the machine panel — separate from the amplifier's control supply and servo output. Panel design must include a suitably rated 24V supply, a relay with contacts rated for the coil current, surge suppression across the coil terminals, and interlock logic coordinating brake release and engagement with the amplifier's servo enable sequence.

Opening the brake — release sequence. Servo must reach enabled and servo-lock state before the brake coil is energised and the shaft is released. A heavy vertical axis at 3.5kW that releases its brake before the amplifier has established position lock will move under gravity until the amplifier catches up. Depending on load mass and travel, this slip can be large enough to trigger a following error alarm, cause a mechanical collision, or produce a position error that disrupts the production sequence. The MBR (Magnetic Brake Release) output on the MR-J2S-350 amplifier provides an amplifier-managed signal specifically for sequencing the brake relay — the amplifier signals when servo lock is confirmed. Wiring the brake relay to MBR ensures the sequence is correct without additional PLC logic.

Closing the brake — engagement sequence. The correct three-step procedure: decelerate the axis to rest under servo control, engage the brake coil to hold the stopped position mechanically, then remove servo enable. Applying the brake to a moving shaft — even slowly — generates friction heat in the disc assembly and accelerates wear. On a 3.5kW axis completing many servo-on/servo-off cycles per shift, following this sequence consistently extends brake service life from years to many more years.

Surge suppression is not optional. The brake coil is an inductive load. When the relay de-energises and cuts coil current, the collapsing magnetic field generates a voltage spike that will damage relay contacts and potentially couple noise into adjacent control electronics if not absorbed. A flyback diode across the 24V DC coil — the standard solution for DC inductive loads — is mandatory. Size it for the coil voltage and current; the motor instruction manual and relay manufacturer's data provide the reference values.

Absolute Encoder on a Braked Vertical Axis: The Full Picture

The 17-bit serial absolute encoder at 131,072 ppr earns its value differently on a braked vertical axis than on a horizontal positioning axis, and the difference is operationally significant.

On a horizontal axis, the absolute encoder's main advantage is eliminating the homing routine at startup — the machine knows where the axis is without moving it. Useful, but not operationally critical.

On a braked vertical axis, the same capability is directly linked to safe and efficient machine restart after any stop event. When an E-stop occurs mid-cycle on a vertical axis, the brake engages and the axis holds mechanically. The encoder retains the exact absolute shaft angle — including accumulated multi-turn count — backed by the A6BAT battery in the MR-J2S-350 amplifier throughout the power-off period. When panel power returns, the amplifier reads the absolute position immediately. The controller knows exactly where the axis stopped. Servo lock is established. The brake releases in the correct sequence. The machine resumes from the exact stopped position without any preliminary movement.

Compare this to an incremental encoder on the same axis: the brake holds the axis safely, but the encoder has lost its position reference. Before production can resume, the axis must execute a homing routine — which on a vertical axis carrying a load means moving the load toward or through the home sensor position. On machines where that homing movement requires clearing the work area, where the tooling or fixture is still in place from the stopped cycle, or where the home position sensor is in a location the loaded axis must move through, this homing requirement is not a minor inconvenience. It is a production interruption that requires human intervention to manage safely.

The absolute encoder eliminates all of this. The brake holds; the encoder remembers; the restart is immediate and fully automated.

Battery maintenance note. The A6BAT in the MR-J2S-350 amplifier maintains the multi-turn counter. Replace it at the first low-battery alarm. Allowing full depletion resets the counter — and on a braked vertical axis where homing requires work area clearance and manual supervision, that reset produces exactly the production interruption a timely battery replacement would have prevented.

Compatible Amplifiers

The HC-SFS353B pairs with the MR-J2S-350 amplifier family — the 3.5kW J2-Super platform. Three interface variants:

MR-J2S-350A is the general-purpose interface amplifier. It accepts pulse-train position commands from CNC controllers and PLCs, plus analog speed and torque references. Position, speed, torque, and all switched control modes are available. RS-232C connects to MR Configurator for commissioning and diagnostics. For machine tool Z-axes, general industrial vertical positioning, and any application where the axis command source is an external CNC or PLC, this is the standard choice.

MR-J2S-350B connects to Mitsubishi A-series and Q-series motion controllers via SSCNET fiber-optic serial bus. All axis commands and feedback data travel over the fiber link. For coordinated multi-axis machines — a Z-axis that must move in defined geometric relationship with X and Y axes on a machining centre, a vertical gantry axis synchronised with horizontal transfer axes on a transfer machine — the SSCNET bus provides the real-time axis coupling that pulse and analog interfaces cannot match. The interlock for the spring-applied brake can be managed through the motion controller's axis-enable output in SSCNET configurations.

MR-J2S-350CP provides built-in single-axis positioning with up to 31 stored point-table positions, activated by digital I/O or CC-Link network command. For standalone vertical positioning axes — servo-driven press feeds, indexed vertical lift stations, independent Z-axis modules on assembly equipment — that do not require real-time coordination with other axes, the CP provides the positioning intelligence locally without a dedicated motion controller.

All three variants include the MBR (Magnetic Brake Release) output for brake relay sequencing, real-time auto-tuning, adaptive vibration suppression, and the full J2-Super protective function suite.

Compatibility notes. The HC-SFS353B requires an MR-J2S-350 amplifier. It is not compatible with the first-generation MR-J2-350 amplifier, which cannot read the 17-bit J2-Super encoder serial protocol. For machines running original MR-J2-350 hardware, the HC-SF353B (same mechanical specification with spring-applied brake, 14-bit encoder) is the correct motor. Not compatible with MR-J3 or MR-J4 amplifiers without a renewal adapter kit.

HC-SFS 3000 rpm Braked Family: The 353B at the Top

The HC-SFS353B is the highest-capacity braked motor in the HC-SFS 3000 rpm range and the only one on the 176 × 176 mm flange. Every other braked motor in this 3000 rpm family fits the compact 130 × 130 mm frame. The 353B's step up to the larger frame reflects the physical requirements of a 3.5kW motor and the increased rotor inertia and stator volume that come with it.

Within the 3.5kW capacity at 3000 rpm, the shaft-and-brake matrix includes: straight shaft no brake (HC-SFS353), straight shaft with brake (HC-SFS353B), keyed shaft no brake (HC-SFS353K), and keyed shaft with brake (HC-SFS353BK). All four use the MR-J2S-350 amplifier. The choice between straight and keyed shaft is determined by the coupling hub design; the choice between brake and no brake is determined by whether the axis carries a gravitational load.

Typical Applications

Vertical Z-axis on large CNC drilling and milling centres. Z-axis drives on large-format CNC machining centres, gantry drills, and vertical boring machines where the spindle head mass and tooling weight create a gravitational load that must be held mechanically at rest. The 11.1 Nm continuous torque sustains Z-feed forces during drilling and boring operations; the spring-applied brake holds the spindle head at every tool change and machine-off event; the absolute encoder eliminates homing on restart.

Servo-driven press ram and die cushion axes. Servo-actuated press ram drives, die cushion servo axes, and blanking press slide drives where the ram carries significant mass with a gravitational component and must hold position precisely at any point in the stroke during setup stops, tooling changes, and emergency stops. The 3,000 rpm rated speed suits direct-coupled ball-screw press feed mechanisms at practical approach and withdrawal speeds.

High-speed vertical transfer and lift stations. Part lift mechanisms, vertical transfer stations, and elevator axes on assembly and machining cells where cycle time is a priority and the 3,000 rpm motor allows faster vertical traversal than a 2,000 rpm motor at equivalent torque. The spring-applied brake holds the lift at every station during station dwell operations; the absolute encoder returns the lift to exact known position after any interruption.

Inclined feed axes on machining and forming equipment. Angled slide axes on profile machining centres, inclined transfer mechanisms, and tilted axis drives on forming equipment where the axis weight component creates a sustained gravitational torque demand. The spring-applied brake holds the inclined axis at any position in the stroke when servo is off; the 70% gravitational load guideline governs the maximum sustainable incline angle at this motor's torque rating.

Heavy rotary table tilting drives. Trunnion axes and tilting rotary table drives on 5-axis machining centres where the combined table-and-workpiece mass creates a gravitational torque component at all angles other than perfect balance. At 3,000 rpm with 11.1 Nm continuous, the tilting drive handles moderate table masses at practical repositioning speeds, and the spring-applied brake holds the table at any angle with the servo off.

Frequently Asked Questions

Q1: What is the difference between the HC-SFS353B and the HC-SFS352B?

Both are 3.5kW braked J2-Super motors on a 176 × 176 mm flange with straight shafts and 17-bit encoders. The difference is the rated speed and its consequence for torque. The HC-SFS352B runs at 2,000 rpm and delivers 16.7 Nm continuously. The HC-SFS353B runs at 3,000 rpm and delivers 11.1 Nm continuously. Same power, different speed-torque balance. Choose the HC-SFS353B when the axis needs shaft speed — high rapid traverse rates, direct ball-screw coupling at fast linear speeds. Choose the HC-SFS352B when the axis needs sustained torque at moderate speed. Both use the MR-J2S-350 amplifier and are mechanically interchangeable on the same 176 × 176 mm mounting frame.

Q2: What sequencing is required when releasing the brake at machine startup?

The MR-J2S-350 must be enabled and servo lock must be established before the brake coil is energised and the shaft is released. Releasing the brake before servo lock allows the gravitational load to move the axis before the amplifier can respond. The MBR (Magnetic Brake Release) output on the amplifier manages this sequence automatically when wired to the brake relay — it signals when servo lock is confirmed and the brake can safely release. Always consult the MR-J2S-350 instruction manual for the specific timing parameters relevant to your axis load and inertia.

Q3: Can the HC-SFS353B replace an HC-SF353B on a machine running an MR-J2-350 amplifier?

Mechanically yes — both motors share the same 176 × 176 mm flange, shaft dimensions, and brake connector arrangement. The amplifier compatibility is the deciding factor. The HC-SF353B has a 14-bit encoder compatible with both MR-J2-350 and MR-J2S-350 amplifiers. The HC-SFS353B has a 17-bit encoder requiring an MR-J2S-350 amplifier only. Installing the HC-SFS353B on a machine running an original MR-J2-350 amplifier will produce an encoder communication fault. Match motor generation to amplifier generation.

Q4: Where is the absolute encoder backup battery, and what are the consequences of full depletion?

The Mitsubishi A6BAT lithium cell is inside the MR-J2S-350 servo amplifier, not in the motor. It maintains the multi-turn absolute counter through all power-off periods. On a braked vertical axis, full battery depletion resets the counter — the axis holds mechanically via the spring-applied brake, but the absolute position is lost. On the next startup, a reference-return cycle is required before the axis can resume production. On vertical axes where homing requires clearing the work area or manual supervision, this is a meaningful production interruption. Replace the A6BAT at the first low-battery alarm from the amplifier — do not defer.

Q5: Is the HC-SFS353B still available, and what is the current-generation upgrade path?

The HC-SFS353B is discontinued by Mitsubishi but remains available through industrial automation surplus dealers and Mitsubishi servo specialist suppliers as new old stock and tested refurbished units. For machines committed to J2-Super hardware, this sourcing path is well established. For new machine designs or full platform upgrades, the current-generation braked equivalent is the HG-SR352BK or HG-SR353B (MR-J4 series, 3.5kW, spring-applied brake, 176 × 176 mm flange, 22-bit encoder, IP67) paired with an MR-J4-350 amplifier. Both motor and amplifier must be replaced together as the encoder protocols are incompatible between generations.