Mitsubishi HC-SFS202K (HCSFS202K) — 2kW AC Servo Motor, Keyed Shaft, No Brake, MELSERVO-J2S Series

Product Identification

Part Number: HC-SFS202K

Also Searched As: HCSFS202K, HC-SFS-202K

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

Motor Type: AC Brushless Servo Motor — Keyed Shaft, No Brake, 2000 rpm

Condition: New In Box, Factory Sealed

The Case for a Keyed Shaft Without a Brake

Most servo motor selection decisions focus on power and torque. The shaft configuration and brake presence are secondary — until they are not. The HC-SFS202K answers a specific pairing of requirements: an axis that needs a positive shaft-to-coupling connection through a machined keyway, and where the application design does not require a fail-safe mechanical hold on servo-off. No brake means simpler wiring, no MBR sequencing overhead, and no additional thermal load in the panel from a brake coil relay circuit. The keyed shaft means a torque path that does not depend on friction alone between hub and shaft.

That combination suits a broad middle ground in industrial servo applications — horizontal axes, belt and chain drives, gear-coupled mechanisms, and any drive where the load is laterally supported, gravity is not a factor in the direction of motion, and a coupling interface that positively transmits torque under reversing and cyclic loads is the engineering preference.

Built on the MELSERVO-J2S platform, the HC-SFS202K carries the full J2-Super specification: 17-bit serial absolute encoder at 131,072 positions per revolution, 9.55 Nm continuous rated torque, 28.6 Nm peak, and all the closed-loop bandwidth improvements that the MR-J2S amplifier's faster processor extracts from the higher-resolution feedback signal. This is not a stripped-down variant — removing the brake takes nothing away from the motor's performance. It removes a mechanical subsystem that was never needed for this application class in the first place.

Technical Specifications

Keyed Shaft: Why It Matters at 2kW

A straight shaft and a keyed shaft transmit torque through fundamentally different mechanisms. On a plain straight shaft, the hub bore clamps around the shaft OD, and friction between the two surfaces carries the torque. The clamp force — generated by the hub's split-clamp or interference fit — must be sufficient to resist the peak torque under the worst operating condition. If it is not, the hub slips, the servo axis loses position, and depending on the application, the consequences range from a scrapped part to a machine fault.

The keyway on the HC-SFS202K changes the mechanics entirely. A key fits a matched slot machined into both the shaft and the hub bore; under load, the key bears in shear across its cross-section and transmits torque directly between shaft and hub. Friction still contributes — the hub should still be properly fitted — but the primary torque path is the key, not the clamp. Under reversing loads, cyclic loading, and shock inputs, a keyed connection remains reliable where a friction-only interface might develop micro-slip over time.

At 9.55 Nm continuous and 28.6 Nm peak, the loads on the HC-SFS202K shaft are not negligible. The peak torque is what matters for coupling selection, and 28.6 Nm at the shaft of a 2,000 rpm motor cycling repeatedly through acceleration, cutting load, and deceleration is exactly the type of duty where keyways have always been the preferred engineering solution.

Common applications that specify keyed shafts at this capacity:

Timing belt drives where the driven pulley must remain absolutely clocked to the shaft through high belt tension and cyclic torque reversals. Gear drives where the pinion or gear hub must transfer torque without any relative rotation that would shift mesh phasing. Chain sprocket drives where the sprocket must maintain fixed angular relationship to the shaft under repeated shock loading from chain engagement. Clutch-type mechanisms where a positive engagement between shaft and driven component is part of the operating principle.

Installation guidance from Mitsubishi's servo motor manual: always use the shaft-end threaded hole to draw the hub axially onto the shaft — a drawbolt, washer, and nut against the hub face pulls it squarely into position. Do not hammer or press-drive hubs onto the shaft. At the HC-SFS202K's frame size, shaft impact during hub installation transmits directly to the encoder disc at the motor's rear. The damage is not always immediately obvious, but it can cause intermittent encoder alarms under vibration that are difficult to trace and expensive to diagnose.

No Brake: What Servo Lock Provides Instead

Without an electromagnetic brake, the HC-SFS202K holds axis position through amplifier servo lock — the control loop remains active, monitoring encoder feedback and supplying corrective current to maintain zero position error. Under normal operating conditions, servo lock is highly effective; the 17-bit encoder provides the fine-grained position data the MR-J2S amplifier needs to minimise position drift at any hold condition.

The relevant question for any application is what happens when servo lock disappears — on an e-stop, an alarm trip, a power fault, or a planned machine shutdown. For horizontal axes carrying a symmetrically loaded mechanism, the axis simply coasts to rest under the amplifier's dynamic brake function and stays there, driven by the small frictional forces in the drive train. No mechanical hold is necessary because no unbalanced force is pushing the axis in any direction.

Where that picture changes — where gravity, preload springs, or asymmetric friction could move the axis on servo-off — the HC-SFS202K is the wrong specification. Those axes belong to the HC-SFS202BK (brake and keyway) or HC-SFS202B (brake, straight shaft). The no-brake HC-SFS202K is the right motor precisely when a mechanical hold system would add complexity, wiring overhead, and panel components that the application simply does not need.

One area where the absence of a brake genuinely simplifies the system: multi-axis machines with many servo axes. Each brake adds a relay, brake cable, surge absorber, and 24V DC power draw. On a machine with twelve or sixteen servo axes, eliminating brakes from the axes that do not need them measurably reduces panel complexity. The HC-SFS202K contributes to that simplification on every horizontal axis in the system.

17-Bit Encoder: J2-Super Feedback at 2000 rpm

The MELSERVO-J2S platform's defining encoder upgrade — from the 14-bit (16,384 ppr) device in the HC-SF series to the 17-bit (131,072 ppr) device in the HC-SFS series — applies fully to the HC-SFS202K. Eight times the encoder resolution changes the quality of every signal that the MR-J2S amplifier computes from position data.

Velocity estimation benefits most directly. The amplifier derives velocity from consecutive position samples. With 131,072 positions per revolution available, each sample covers a fine angular increment at 2,000 rpm, giving the speed loop a low-noise velocity estimate to work with. That clean estimate allows higher proportional gains in the speed loop without exciting mechanical resonances, which translates to tighter velocity regulation and faster disturbance rejection during cutting loads and axis reversals.

Position loop performance improves correspondingly. The fine resolution allows the control loop to detect and correct very small position deviations — tool deflection compensation, thermal growth correction, lead screw backlash management — with a level of sensitivity that 14-bit feedback cannot match.

The absolute function is maintained by the A6BAT lithium battery inside the MR-J2S amplifier. The battery holds the multi-turn absolute position counter through any power interruption, planned or unplanned. Restart after overnight shutdown, e-stop recovery, or alarm reset brings the axis up in its last known absolute position without any reference return movement. For tight production schedules where restart time matters, this is a concrete time saving across every shift.

Compatible Amplifiers

The HC-SFS202K pairs with the MR-J2S-200 class amplifier. Three variants cover the main control architectures used on the J2-Super platform:

MR-J2S-200A takes analog and pulse-train commands from CNC systems and PLCs. Position, speed, and torque control modes are all available. Setup and monitoring through MR Configurator (MRZJW3-SETUP) via RS-232C.

MR-J2S-200B operates over SSCNET fiber-optic serial bus under a Mitsubishi motion controller — A-series or Q-series. Multi-axis coordinated motion with interpolation is handled at the controller level; the amplifier executes trajectory commands received over the network using local encoder feedback.

MR-J2S-200CP incorporates a built-in positioning function, storing up to 31 target positions internally. CC-Link or I/O commands select targets and trigger moves, making this variant suitable for standalone positioning without a dedicated motion controller.

All three variants fully support the HC-SFS202K's 17-bit encoder and 11A rated current. The HC-SFS202K is not compatible with original MR-J2-200 (first-generation, pre-J2S) amplifiers, which cannot interpret the 17-bit encoder format, nor with MR-J3 or MR-J4 amplifiers. Where the installed amplifiers are first-generation MR-J2, the HC-SF202K (J2 motor with 14-bit encoder) is the correct sourcing target.

Where the HC-SFS202K Fits in the HC-SFS 2000 rpm Family

The HC-SFS202K steps up from the 130 × 130 mm flange group to the 176 × 176 mm flange — the same mounting footprint shared by every model from 2kW through 7kW in this family. A machine designed around this flange size can accommodate motor capacity upgrades within that range without mounting plate changes.

The "K" suffix consistently denotes keyed shaft across the entire HC-SFS family. Every capacity from 500W to 7kW is available in keyed-shaft form, and within each capacity, the keyed straight-shaft no-brake variant pairs mechanically with the same flange and electrically with the same amplifier as the straight-shaft variant. The shaft choice has no effect on amplifier selection.

Typical Applications

Timing belt drive axes on machine tools. Tool magazine indexing drives, pallet shuttle belts, and conveyor transfer axes using toothed timing belt interfaces require keyed shaft pulleys to prevent belt tension and cyclic tooth engagement forces from rotating the pulley relative to the shaft. At 9.55 Nm continuous, the HC-SFS202K handles medium-format toolchanger and pallet mechanism loads well within its thermal rating.

Gear-driven auxiliary axes. CNC rotary table auxiliary drives using gear coupling between the servo shaft and table input, and gear-driven feed mechanisms in specialised machine tools, need the keyed shaft for a positive, play-free gear hub connection. The 28.6 Nm peak provides the acceleration torque for fast indexing while the 9.55 Nm continuous covers sustained rotary motion.

Ball screw feed axes with gear coupling. On machining centres where a gear reduction sits between the servo motor and the ballscrew input, the motor side of the gear coupling typically uses a keyed interface. The HC-SFS202K's keyed shaft provides that connection, and the J2-Super encoder's fine resolution feeds back through the gear ratio to give the position loop high effective resolution at the table.

Horizontal conveyor and transfer drives. Servo-driven conveyor indexing on automated assembly lines, part transfer systems, and palletising equipment uses medium-capacity servo motors on horizontal transfer axes. These are exactly the axes where a brake is unnecessary — the load is horizontally supported, and the conveyor holds position through mechanical friction when servo lock is released — and where a keyed shaft suits the sprocket or coupling drive design.

Winding and tension control axes. Material handling axes running in torque control mode to regulate web tension or winding torque use the servo motor's current command as the torque reference. The HC-SFS202K's 17-bit encoder provides the smooth, low-ripple velocity feedback that torque control mode requires to regulate tension without oscillation across a wide speed range.

New In Box, Factory Sealed

Factory sealed means original Mitsubishi packaging with all protective covers undisturbed — the shaft keyway and key slot are protected by the shaft-end cap, the encoder connector and power connector ports remain sealed, and the oil seal at the shaft through-point is in as-manufactured condition. The motor has never been installed, never powered, and carries no mechanical or thermal history.

For machines currently stopped waiting on this part, in-stock new-in-box removes repair lead time from the critical path entirely. For planned maintenance stock, factory-sealed units store correctly for multiple years under stable temperature and low-humidity conditions. Beyond five years in storage, a slow manual shaft rotation as part of a pre-installation check helps redistribute bearing grease before the motor is placed in service.

Frequently Asked Questions

Q1: Which amplifiers are compatible with the HC-SFS202K?

The HC-SFS202K requires a MR-J2S-200 class amplifier. The three standard variants are the MR-J2S-200A (general-purpose analog/pulse command, position/speed/torque control), MR-J2S-200B (SSCNET fiber-optic bus for Mitsubishi motion controllers), and MR-J2S-200CP (built-in point-table positioning with CC-Link). All support the 17-bit serial encoder. The HC-SFS202K is not compatible with first-generation MR-J2-200 amplifiers or with MR-J3 / MR-J4 amplifiers.

Q2: What is the difference between the HC-SFS202K and the HC-SFS202BK?

The two motors are identical in every electrical and mechanical specification — 2kW, 9.55 Nm, 28.6 Nm peak, 17-bit encoder, keyed shaft, 176 × 176 mm flange, same amplifier requirement. The only difference is that the HC-SFS202BK has a spring-applied electromagnetic brake; the HC-SFS202K does not. Choose the no-brake HC-SFS202K for horizontal axes and any application where servo lock is sufficient at all stop conditions. Choose the HC-SFS202BK when the axis carries a gravity load or requires fail-safe mechanical hold on servo-off.

Q3: What is the difference between the HC-SFS202K and the HC-SFS202 (straight shaft)?

Mechanically and electrically identical — same output, torque, encoder, flange, and amplifier class. The only difference is the shaft interface. The HC-SFS202 has a plain straight shaft for friction-clamp couplings. The HC-SFS202K has a machined keyway for positive key-and-hub torque transmission. Choose based on the coupling design of the driven mechanism. There is no performance difference between the two shaft types under correctly installed coupling conditions.

Q4: Can the HC-SFS202K replace a HC-SF202K from the older J2 generation?

Both motors share the same 176 × 176 mm flange and are mechanically interchangeable at the mounting interface. However, the encoder generations differ: the HC-SF202K uses a 14-bit encoder and is compatible with both MR-J2 and MR-J2S amplifiers. The HC-SFS202K uses a 17-bit encoder and requires MR-J2S amplifiers. If the machine runs first-generation MR-J2-200 amplifiers, the HC-SFS202K will not operate — source the HC-SF202K instead. If the amplifiers are MR-J2S-200, the HC-SFS202K is a direct drop-in replacement with higher feedback resolution.

Q5: Is a key supplied with the HC-SFS202K?

Mitsubishi's standard practice for keyed-shaft HC-SFS motors is to supply the key separately from the shaft — the keyway is machined into the shaft, but the key itself is typically not included in the motor packaging. Verify key dimensions against the shaft and hub keyway specifications before assembly, and use a properly fitted key with correct tolerance for the application's torque and shock loading conditions. Refer to the relevant Mitsubishi servo motor instruction manual for shaft dimensions and recommended key specifications for the HC-SFS202 frame size.