One New Mitsubishi Servo Motor HC-SFS502BK HCSFS502BK HC-SFS502BK New In Box Factory Sealed

Mitsubishi HC-SFS502BK (HCSFS502BK) — 5kW AC Servo Motor, Keyed Shaft + Brake, MELSERVO-J2S Series

Product Identification

Part Number: HC-SFS502BK

Also Searched As: HCSFS502BK, HC-SFS-502BK

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

Motor Type: AC Brushless Servo Motor — Keyed Shaft with Electromagnetic Brake, 2000 rpm

Condition: New In Box, Factory Sealed

Built for Axes That Cannot Afford to Slip or Drift

Two requirements define the HC-SFS502BK precisely: a driven mechanism that needs a positive key-and-hub torque connection, and an axis design that demands fail-safe mechanical hold when servo power is removed. At 5kW, 23.9 Nm continuous, and 71.6 Nm peak, this motor sits at the capacity level where both of those requirements carry real engineering weight — where a slipping coupling is not a recoverable nuisance but a production-stopping fault, and where an unbraked axis losing servo control under load is a genuine safety concern.

The keyed shaft and the spring-applied electromagnetic brake are independent solutions to independent problems. The keyway addresses the torque transmission interface: it provides a direct, friction-independent mechanical connection between the motor shaft and the driven component, immune to the micro-slip that can develop in friction-only clamp interfaces under the cyclic, reversing loads of production servo axis operation. The brake addresses what happens when the servo is deliberately or unexpectedly de-energised: the spring engages immediately, the shaft is held mechanically, and the axis does not move regardless of what happens in the control system.

On the MELSERVO-J2S platform, the HC-SFS502BK adds the full J2-Super capability to that mechanical specification: a 17-bit serial absolute encoder at 131,072 positions per revolution, compatibility with MR-J2S-500 amplifiers, and the high-bandwidth closed-loop performance that the J2-Super generation's improved processor architecture makes possible. New in box, factory sealed, in stock.

Technical Specifications

The Keyed Shaft: Positive Torque Transmission at 5kW

At 23.9 Nm continuous and 71.6 Nm peak, the mechanical demands on the shaft-to-hub interface are not trivial. The peak figure is the design load — 71.6 Nm is what the coupling must transmit without any relative movement between shaft and hub under the worst-case operating condition the axis encounters. On a servo axis, that condition is typically a maximum-rate acceleration immediately followed by a sharp reversal, or a rapid deceleration from full rapid traverse speed into an abrupt stop. Neither of these is unusual in CNC machine tool operation; both happen repeatedly across a production shift.

On a plain straight shaft, the hub transmits torque through friction. The clamp force between hub bore and shaft OD must be sufficient to prevent slip at 71.6 Nm, and that force depends on hub bore tolerance, shaft surface finish, clamping fastener torque, and the absence of any contamination at the interface. Every one of these factors can degrade over time in a production environment. A marginal clamp that handles the first year of service without incident may develop micro-slip in the second year, after vibrational fretting has slightly modified the shaft surface or fastener preload has relaxed.

The keyway changes the fundamental mechanism. Torque flows through the key's shear cross-section — a direct mechanical path that does not degrade with surface condition changes, does not relax with vibration, and does not depend on the quality of any friction interface. Under the reversing and shock loads of servo axis operation, a properly fitted keyed connection is inherently more reliable over a long service life than a friction-clamp interface at the same capacity level.

Where keyways are essentially mandatory at 5kW:

Worm-gear rotary table inputs, where the motor-side gear hub is a keyed bore and the motor shaft must match. Timing belt drive pulleys on large ballscrew axes, where repeated belt tension reversal would eventually rotate a friction-clamped pulley hub. Chain sprocket drives on pallet transfer systems, where chain engagement shock loads are cyclic and directionally asymmetric. Mechanical clutch drive interfaces, where positive angular registration between shaft and driven component is part of the mechanism's operating principle.

Installation: seat the coupling hub using the shaft-end threaded hole and a drawbolt — never by impact. At this motor's mass and shaft cross-section, any axial impact during hub installation transmits directly to the encoder disc at the motor's rear. The resulting damage rarely causes an immediate fault; it tends to produce intermittent encoder alarms months into service, under vibration, with no obvious connection to the original installation event.

The Electromagnetic Brake: Fail-Safe Hold at This Scale

Spring-applied brakes become more consequential as motor capacity increases, because the load capacity increases proportionally. At 5kW driving a large VMC Z-column, a loaded pallet shuttle, or a heavy rotary table mechanism, the energy stored in the axis at rest — gravitational potential or mechanical preload — represents a real hazard if the axis moves unexpectedly when servo current drops to zero.

The HC-SFS502BK's brake is mechanically straightforward: a spring holds the friction disc against the brake plate when 24V DC is absent, and the coil holds it clear when 24V is present. The spring engages on power removal regardless of whether the removal is planned, unplanned, gradual, or instantaneous. There is no control logic in the brake mechanism itself. No software command is required to activate it. No signal path between the controller and the brake can fail in a way that prevents engagement. The brake's default state — when power is absent — is always locked.

At 5kW and the load masses that go with axes of this capacity, that default-locked characteristic matters considerably. A 5kW Z-column drive that loses servo control and has no brake will follow gravity until friction stops it. The distance it travels before stopping is not negligible, and the workpiece, tooling, and fixturing below the column are in that path. The same column with the HC-SFS502BK fitted holds in place the instant the 24V DC is removed — by design during a shutdown sequence, by relay dropout on e-stop, or automatically on power loss.

Three installation requirements at this capacity level:

Always use the MR-J2S amplifier's MBR (electromagnetic brake interlock) output to control the brake relay. The MBR signal times brake engagement to occur after the amplifier has confirmed the motor has decelerated to rest. Engaging the spring against a rotating 5kW motor shaft generates a significant mechanical shock that damages the brake friction surfaces and compresses the expected brake service life from years to a fraction of that in extreme cases.

Fit a surge absorber directly across the brake coil terminals — not at the relay, not mid-cable, but at the coil. The inductive spike generated when 24V DC switches off an unsuppressed coil at this power level is sufficient to damage relay contacts and digital output circuits. The absorber must be positioned close to the coil to be effective.

For vertical and gravity-loaded axes, Mitsubishi's documented guidance places the recommended maximum static unbalanced torque at or below 70% of the motor's continuous rated torque — approximately 16.7 Nm for this motor. Axis designs with higher unbalanced gravitational torque at the motor shaft should incorporate mechanical counterbalancing to supplement the servo and brake system rather than relying on them alone.

17-Bit Encoder: J2-Super Resolution in a 5kW Package

The transition from HC-SF502BK (J2 generation, 14-bit, 16,384 ppr) to HC-SFS502BK (J2S generation, 17-bit, 131,072 ppr) is an eight-fold encoder resolution increase on otherwise identical hardware. At 5kW and 2,000 rpm, the effects are practical rather than theoretical.

Velocity estimation accuracy improves proportionally with resolution. The MR-J2S amplifier derives velocity from successive encoder position samples at a fixed sample interval. With 131,072 positions available per revolution, each inter-sample increment is eight times finer than with 16,384 ppr, and the velocity estimate the speed loop receives is correspondingly cleaner. A cleaner velocity signal supports higher proportional gain in the speed loop without instability, and higher gain means faster rejection of disturbances — cutting forces, load changes, and transmission compliance effects that push the axis velocity off its commanded profile.

Low-speed performance also improves. On axes running slow feed rates — contouring operations, fine-finish boring, thread cutting — the encoder's resolution directly affects how smoothly the speed loop can regulate velocity. Coarser position increments at low speed produce velocity ripple that appears in the machined surface as a periodic pattern. The 17-bit encoder reduces that ripple substantially, an effect that shows clearly in surface finish on precision slow-feed operations at this capacity level.

The absolute function carries its value regardless of encoder resolution. The A6BAT lithium battery in the MR-J2S amplifier maintains the multi-turn absolute position counter indefinitely through any power interruption. Every restart — after a planned shutdown, an e-stop recovery, or an alarm reset — brings the axis up in exact absolute position. No reference return required, no production time lost to mandatory homing cycles.

Compatible Amplifiers

The HC-SFS502BK requires the MR-J2S-500 class amplifier. Three variants cover the main system architectures:

MR-J2S-500A — General-purpose interface, accepting analog velocity commands and pulse-train position commands from CNC systems and PLCs. Supports position, speed, and torque control modes. Setup and monitoring via MR Configurator through RS-232C.

MR-J2S-500B — SSCNET fiber-optic serial bus interface for Mitsubishi motion controllers. Coordinated multi-axis interpolation with trajectory commands delivered over the network from A-series or Q-series motion controllers. The standard choice for machine designs with all servo axes under coordinated motion control.

MR-J2S-500CP — Built-in positioning function with stored point table. Up to 31 target positions stored in the amplifier, activated by I/O or CC-Link commands. Suited to standalone positioning applications without a dedicated motion controller.

All three variants support the 17-bit encoder and are rated for 25A continuous. The HC-SFS502BK is not compatible with original MR-J2-500 amplifiers — the J2S encoder protocol is unreadable by first-generation J2 hardware. It is also not compatible with MR-J3 or MR-J4 amplifiers. For machines running original MR-J2-500 hardware, the HC-SF502BK (J2 generation, 14-bit encoder, same mechanical specification) is the correct sourcing target.

HC-SFS502BK in the HC-SFS 2000 rpm Range

Within the 502 capacity point, four suffix variants cover the complete shaft-and-brake matrix:

All four share the same 176 × 176 mm flange, 17-bit encoder, 23.9 Nm / 71.6 Nm torque figures, and MR-J2S-500 amplifier requirement. The shaft type and brake presence do not affect any electrical specification.

Typical Applications

VMC Z-axis on large vertical machining centres with gear or belt coupling. The gravity-loaded spindle head axis is the canonical application for the BK suffix: mechanical hold on servo-off is non-negotiable, and where the Z-axis ballscrew drive uses a toothed belt or gear reduction between the motor and ballscrew input shaft, the keyed motor shaft is the correct interface for the drive pulley or gear hub. The HC-SFS502BK satisfies both requirements in a single package.

HMC pallet shuttle drives with keyed sprocket interface. Pallet changers on horizontal machining centres use chain or belt shuttle drives where the motor-side sprocket or pulley is keyed to the motor shaft. The shuttle carries substantial pallet mass and must hold position firmly at each transfer station — brake engaged during clamping and unclamping operations, keyed shaft ensuring the drive component stays clocked to the motor shaft through repeated high-torque shuttle cycles.

Large rotary table and trunnion indexing drives. 4th and 5th-axis rotary table drives using worm gear or direct gear reduction between the servo motor and the table typically specify keyed motor-side gear hubs. The axis must hold angular position mechanically during cutting operations; the brake provides that hold while the cutting forces act on the table. The absolute encoder guarantees angular positioning accuracy on every index cycle without a reference return.

Servo-driven vertical actuators and lift mechanisms. Industrial vertical lift axes — workpiece lifts, tombstone elevator systems, pallet hoists — combine the need for high continuous torque, fail-safe brake hold, and a positive shaft coupling interface into exactly the specification the HC-SFS502BK covers. The motor-side drive connection is typically a keyed hub on a gear reduction or lead screw drive, and the brake holds the load at height through all power-off events.

Transfer line station drives with mechanical registration. Transfer machine servo station drives that use keyed sprocket or gear drives to index part fixtures through sequential machining operations need both the positive shaft connection that prevents registration drift over thousands of cycles and the brake that holds each station position during the machining dwell. Absolute encoder position feedback ensures the station index is confirmed accurate on every cycle.

New In Box, Factory Sealed

Factory sealed means original Mitsubishi packaging with all protective covers in place — shaft-end cap protecting the keyway and key slot, encoder and power connector ports covered, oil seal intact, and inner foam packing undisturbed. The motor and integrated brake assembly have never been powered or installed. No thermal history, no bearing wear, no brake disc cycling from prior service.

For a machine currently stopped waiting on this part, in-stock new-in-box delivers a known-condition unit immediately without repair turnaround time or the uncertainties that come with refurbished components. For planned spare parts stock on operations where this capacity and configuration appears on multiple critical axes, factory-sealed units provide consistently commissionable inventory.

At the weight typical of the 5kW frame with brake assembly, the HC-SFS502BK ships in packaging proportioned to its mass. Stored under stable temperature, low humidity, and away from vibration, factory-sealed stock maintains full specification over several years. Beyond five years, a slow pre-commissioning shaft rotation as part of the installation inspection helps redistribute bearing grease before the motor enters service.

Frequently Asked Questions

Q1: Which amplifiers are compatible with the HC-SFS502BK?

The HC-SFS502BK requires a MR-J2S-500 class amplifier from the MELSERVO-J2S platform. The three main variants are the MR-J2S-500A (general-purpose analog/pulse command), MR-J2S-500B (SSCNET fiber-optic bus for Mitsubishi motion controllers), and MR-J2S-500CP (built-in point-table positioning). All support the 17-bit encoder and 25A rated current. This motor is not compatible with original MR-J2-500 amplifiers or with MR-J3 / MR-J4 amplifiers.

Q2: What is the difference between the HC-SFS502BK and the HC-SF502BK?

Both motors are 5kW, 23.9 Nm, keyed shaft with electromagnetic brake, on a 176 × 176 mm flange — physically interchangeable at the mount. The distinction is the encoder generation: the HC-SF502BK uses a 14-bit encoder (16,384 ppr) and works with MR-J2 and MR-J2S amplifiers. The HC-SFS502BK uses a 17-bit encoder (131,072 ppr) and requires MR-J2S amplifiers only. If the machine runs original MR-J2-500 hardware, source the HC-SF502BK. If it runs MR-J2S-500, both motors are compatible.

Q3: How should the electromagnetic brake be wired and sequenced correctly?

The brake is spring-applied and fail-safe — 24V DC holds it open, spring closes it on power removal. It is a holding device, not a stopping brake, and must only engage after the motor has stopped. Always control the brake relay through the MR-J2S amplifier's MBR (brake interlock) output, which times brake engagement after the amplifier confirms the motor has decelerated to rest. Engaging the brake against a rotating 5kW shaft causes rapid brake wear and mechanical shock. Also fit a surge absorber directly across the brake coil terminals to suppress inductive voltage spikes at switch-off.

Q4: Does the 17-bit encoder battery sit inside the motor or the amplifier?

The battery is in the servo amplifier, not the motor. The Mitsubishi A6BAT lithium cell installed inside the MR-J2S-500 amplifier maintains the multi-turn absolute position counter through power-off periods. Replace it when the amplifier displays its low-battery alarm — before full depletion. A completely discharged A6BAT resets the absolute position counter, requiring a reference return cycle before production can resume. The motor itself requires no battery and no battery-related maintenance.

Q5: What is the correct way to fit a coupling hub onto the keyed shaft?

Use the threaded hole at the shaft end to draw the hub axially onto the shaft with a drawbolt, washer, and nut bearing against the hub face. Never hammer or press-drive the hub onto the shaft. At this motor's frame size, impact loads during hub fitting travel through the shaft to the encoder assembly at the rear of the motor and cause damage that typically does not produce an immediate fault — it surfaces later as intermittent encoder alarms under vibration, which are difficult to diagnose. The drawbolt method is straightforward, takes slightly longer, and prevents this failure mode entirely.