Mitsubishi HC-SFS353K (HCSFS353K) — 3.5kW AC Servo Motor, Keyed Shaft, 3000 rpm, MELSERVO-J2S Series

Product Identification

Part Number: HC-SFS353K

Also Searched As: HCSFS353K, HC-SFS-353K

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

 Motor Type: AC Brushless Servo Motor — Keyed Shaft, No Brake, 3000 rpm

Condition: New In Box, Factory Sealed

What Makes This Motor Different

The HC-SFS family runs at two rated speeds: 2,000 rpm and 3,000 rpm. Models ending in "2" are the 2000 rpm variants. Models ending in "3" — including the HC-SFS353K — are rated at 3,000 rpm. At 3.5kW output with a rated torque of 11.1 Nm and a 176 × 176 mm flange, this motor offers the same physical footprint as the 2000 rpm HC-SFS352 but a higher top speed, making it the right choice wherever the application trades some continuous torque headroom for faster rapid traverse, quicker index cycles, or higher spindle-adjacent axis speeds.

The "K" suffix means keyed shaft — a machined keyway cut into the motor shaft for positive torque-transmitting connection to coupled components. No brake is fitted; this motor holds position through closed-loop servo lock from the amplifier. Applications that need a fall-safe mechanical hold on servo-off belong to the HC-SFS353BK variant. The HC-SFS353K is the specification for horizontal axes, angular positioning tables, and any drive where gravity is not a concern and the coupling interface requires a key.

Backed by the MELSERVO-J2S platform's 17-bit serial absolute encoder and compatible MR-J2S-350 amplifiers, the HC-SFS353K carries the full J2-Super feature set: 131,072 positions per revolution of feedback resolution, absolute position retention through battery backup, and speed loop bandwidth that exceeds what the first-generation J2 amplifiers could achieve.

Technical Specifications

3000 rpm vs 2000 rpm — Understanding the Trade-Off

Both the HC-SFS352 and HC-SFS353 are 3.5kW motors on the same 176 × 176 mm flange. What changes between them is the rated speed, and with it, the continuous torque. At 2,000 rpm, the HC-SFS352 delivers 16.7 Nm continuously. At 3,000 rpm, the HC-SFS353K delivers 11.1 Nm continuously — roughly two-thirds of the lower-speed variant's figure.

That trade-off is deliberate. The power output is nearly the same (both are 3.5kW class). What the 3000 rpm motor gives you in exchange for the lower continuous torque is the ability to run the axis faster — important when machine cycle time is determined by rapid traverse or index speed rather than by cutting force. An axis that spends 80% of its cycle time in rapid positioning and only 20% at cutting feed rates will often benefit more from speed than from the extra torque headroom the 2000 rpm variant provides.

For machine designers choosing between the two: if the worst-case continuous torque demand on your axis exceeds 11.1 Nm, the HC-SFS352 is the safer choice. If the torque budget is comfortably within 11.1 Nm and faster non-cutting moves reduce cycle time meaningfully, the HC-SFS353K earns its specification.

The Keyed Shaft at 3.5kW

Eleven Newton-metres of continuous torque is not trivial. At this capacity, a badly fitted friction-clamp coupling — under-torqued fasteners, inconsistent surface finish on the shaft OD, or a hub bore that is slightly oversized — can develop micro-slip over time. Micro-slip on a servo axis is insidious: it is often too small to trigger a following-error alarm immediately, but large enough to introduce positional drift that accumulates across multiple cycles.

The keyway on the HC-SFS353K eliminates that failure mode. A properly fitted key and hub form a positive shear-load connection; the key transmits the torque directly between shaft and hub rather than relying on clamping friction alone. For timing belt drives, chain sprockets, pinion gears, and couplings that must remain absolutely clocked to the shaft under repeated reversal and shock load, the keyed shaft is the correct engineering specification.

Installation note from Mitsubishi's instruction manual: When fitting a pulley or hub onto a keyed shaft, use the shaft-end threaded hole to draw the component on — insert a double-end stud, place a washer against the hub face, and tighten a nut to pull the hub into position. Do not hammer components onto the shaft. Shock loads from hammering transmit through the shaft to the encoder disc at the motor's rear and can cause encoder damage that is not immediately obvious but shortens service life or causes intermittent faults later.

17-Bit Absolute Encoder — The J2S Advantage

The J2-Super platform introduced the 17-bit (131,072 ppr) serial absolute encoder as standard across the HC-SFS family. Before that, HC-SF motors used a 14-bit device at 16,384 ppr. The resolution improvement is eight-fold, and its effects are practical rather than merely numerical.

At 3,000 rpm — the rated speed of the HC-SFS353K — the encoder sends position data to the amplifier more frequently per unit time than a 2,000 rpm motor simply because the shaft is spinning faster. High resolution means that even at this speed, each individual position update represents a small angular step. The speed loop receives fine-grained velocity information, which supports the higher bandwidth that the MR-J2S amplifier's improved CPU is designed to exploit. The result is better velocity stability at operating speed, tighter following error during acceleration, and improved disturbance rejection during the working cycle.

The absolute functionality keeps doing its job regardless of speed rating. Battery backup in the MR-J2S amplifier — using the A6BAT lithium cell — retains the multi-turn absolute position counter through power-off events. The axis knows exactly where it is on the next power-up, without performing a reference return. For machines that run multiple shifts or restart frequently after planned shutdowns, this is a practical time-saver.

Compatible Amplifiers

The HC-SFS353K pairs with MR-J2S-350 class amplifiers from the MELSERVO-J2S platform. The confirmed compatible models are:

• MR-J2S-350A — General-purpose, analog/pulse command interface. Position, speed, and torque control modes.
• MR-J2S-350B — SSCNET (fiber-optic bus) interface, for motion controller and multi-axis coordinated systems.
• MR-J2S-350CP — Built-in positioning function, suitable for standalone point-to-point applications without an external controller.

All three variants support the HC-SFS353K's 17-bit encoder protocol and are rated for the motor's 16.4A continuous current.

The HC-SFS353K is not compatible with MR-J3 or MR-J4 amplifiers, which use a different encoder interface. It is also not compatible with first-generation MR-J2 amplifiers, which predate the J2S encoder protocol.

HC-SFS 3000 rpm Family — Capacity Reference

Within the HC-SFS 3000 rpm sub-family, the 353K sits at mid-capacity:

All models in this table use the 17-bit serial absolute encoder, 200V AC class supply, IP65 protection, and oil-sealed shaft. The 353 uses the larger 176 × 176 mm flange, consistent with the 2000 rpm HC-SFS352 at the same capacity.

Typical Applications

CNC machining centre high-speed auxiliary axes. Secondary axes on 5-axis machining centres — A-axis trunnion tilts, B-axis table rotation, tool magazine drives — benefit from 3000 rpm motors where fast index time between positions matters more than raw torque at low feed rates. The keyed shaft suits direct or geared drive designs in rotary table mechanisms.

High-cycle conveyor and transfer indexing. Servo-driven transfer systems with short station-to-station distances and high cycle rates use 3000 rpm motors to shorten the acceleration-to-speed phase of each move. Twelve stations cycling every 8 seconds in an automotive assembly cell need fast axis response, not maximum torque at low speed.

Timing belt and chain drives. Packaging lines, labelling machines, and form-fill-seal equipment that use servo-driven timing belt axes typically require keyed shafts on the drive pulley to prevent belt tension from rotating the hub on the shaft. At 3.5kW, the HC-SFS353K provides ample capacity for this type of continuous-production duty.

X-Y positioning tables and gantry systems. Flat-bed servo positioning systems for laser processing, dispensing, or inspection use 3000 rpm motors on high-speed scan axes where constant velocity across long travel distances determines quality. The combination of high resolution and high top speed is exactly the specification for these applications.

Winding and tension-control axes. Material winders and unwinders with medium-capacity cores use 3.5kW servo drives in torque-control mode to regulate web tension. The motor runs across a wide speed range; the 3000 rpm rating provides headroom for high-speed sections of the web path.

New In Box, Factory Sealed

This HC-SFS353K ships as Mitsubishi originally packed it — protective carton intact, shaft and connector covers in place, inner foam cradle undisturbed. Factory sealed means no prior installation, no accumulated thermal history, no handling stress on the keyed shaft or encoder assembly.

For maintenance teams building strategic spares inventory for machines running the J2S platform, new-in-box stock at the 3.5kW 3000 rpm specification is increasingly difficult to source as this product generation moves further into discontinuation. Motors entering service directly from factory-sealed stock carry no performance variables that come with repaired or refurbished units.

For long-term storage: cool, dry, vibration-free conditions preserve full specification across several years. For storage beyond five years, Mitsubishi guidance recommends periodic slow shaft rotation to redistribute bearing grease before the motor is put into service.

Frequently Asked Questions

Q1: What amplifiers are compatible with the HC-SFS353K?

The HC-SFS353K requires a MR-J2S-350 class amplifier. The main variants are the MR-J2S-350A (general-purpose analog/pulse command), MR-J2S-350B (SSCNET fiber-optic bus), and MR-J2S-350CP (built-in positioning function with CC-Link). All are rated at 3.5kW and support the 17-bit serial encoder protocol used by this motor. The HC-SFS353K is not compatible with MR-J3, MR-J4, or original MR-J2 (first-generation) amplifiers.

Q2: What is the difference between the HC-SFS352K and HC-SFS353K?

The two models share the same 3.5kW output, 176 × 176 mm flange, 17-bit encoder, IP65 rating, keyed shaft, and MR-J2S-350 amplifier compatibility — but they run at different rated speeds. The HC-SFS352K is rated at 2,000 rpm with 16.7 Nm continuous torque. The HC-SFS353K is rated at 3,000 rpm with 11.1 Nm continuous torque. Choose the 353K where higher speed is the priority; choose the 352K where continuous torque headroom matters more than maximum axis speed.

Q3: Does the HC-SFS353K have an electromagnetic brake?

No. The HC-SFS353K does not include a brake. Position is maintained at rest through amplifier servo lock — the control loop remains active and holds the axis with motor current. For applications requiring a mechanical fail-safe hold when the servo is de-energised (vertical axes, gravity-loaded arms), the HC-SFS353BK (keyed shaft with spring-applied electromagnetic brake) is the correct variant to specify.

Q4: Does the absolute encoder require a battery, and where is it installed?

Yes. The 17-bit serial absolute encoder retains multi-turn position data during power-off through battery backup. The battery — a Mitsubishi A6BAT lithium cell — is housed inside the MR-J2S servo amplifier, not in the motor. When healthy, it keeps absolute position through any power interruption, eliminating the need for a homing cycle on restart. Monitor the amplifier's low-battery alarm and replace the A6BAT proactively at the next planned maintenance shutdown before full depletion occurs.

Q5: Can the HC-SFS353K replace an HC-SFS352K if the machine needs higher speed?

Both motors mount on the same 176 × 176 mm flange and share the same amplifier class (MR-J2S-350), so the physical swap is possible without mounting changes. However, the speed and torque characteristics differ — the 353K runs faster but produces less continuous torque. Before substituting, verify that the axis torque requirements are comfortably within 11.1 Nm continuous at all points in the duty cycle, and that the existing amplifier parameters (electronic gear ratio, speed limits, acceleration ramps) are updated to reflect the 3000 rpm rated speed. A parameter review in MR Configurator before first power-up after the swap is strongly recommended.