Mitsubishi HC-SF702 (HCSF702) — 7kW AC Servo Motor, Straight Shaft, No Brake, MELSERVO J2 Series

Product Identification

Part Number: HC-SF702

Also Searched As: HCSF702, HC-SF-702

Series: Mitsubishi MELSERVO HC-SF (J2 Generation)

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

Condition: New In Box, Factory Sealed

Overview

The Mitsubishi HC-SF702 is the 7kW straight-shaft, no-brake motor at the top of the original MELSERVO J2 HC-SF range — the largest standard capacity in this medium-inertia family, rated at 33.4 Nm continuous and 100 Nm peak. It is a direct-drive workhorse for heavy machine tool axes: large VMC Z-columns, substantial HMC W-axis systems, high-mass rotary table drives, and any application where the axis load demands maximum output from this motor family.

Two things set the HC-SF702 apart from other 7kW options in the MELSERVO lineup. First, it uses a straight shaft without a keyway, making it the correct specification wherever the coupling interface is a friction-clamp or split-clamp hub design. Second, it carries no electromagnetic brake — there is no spring-applied holding device in this motor. Position is maintained at rest through amplifier servo lock alone. This is the appropriate configuration for horizontal axes and any drive where gravity is not a loading factor and mechanical hold between power cycles is not required by the machine's safety design.

The J2 generation 14-bit serial absolute encoder — 16,384 positions per revolution — provides the feedback signal. While the later HC-SFS702 upgraded to 17-bit, the HC-SF702's 14-bit encoder is fully capable for the demanding applications this motor was designed for, and it retains backward compatibility with both the original MR-J2-700 amplifiers and the later MR-J2S-700 platform — a flexibility the HC-SFS series does not offer.

Technical Specifications

7kW at 2000 rpm: Understanding the Output Numbers

The HC-SF702 generates 33.4 Nm continuously at its rated speed of 2,000 rpm. That combination produces exactly 7kW. It is worth being precise about what 33.4 Nm means at this frame size: it is the torque the motor can sustain indefinitely under rated load, within its thermal limits, when operated within the amplifier's continuous current rating. Not a burst figure. Not a laboratory peak. The torque the axis will see during a sustained machining cut, a slow contouring move, or any prolonged high-load condition.

The 100 Nm peak — three times the continuous rating — is what the amplifier can command during acceleration and deceleration phases. Rapid traverse to a new position, deceleration into a clamp, an aggressive ramp from rest to cutting feedrate: these are the moments when the amplifier calls for peak current and the motor delivers peak torque. After the transient, the motor returns to continuous operating conditions. Thermal management depends on the duty cycle keeping average delivered torque well within the continuous rating; the 100 Nm figure is the ceiling for short-duration bursts, not a sustained capability.

The 10 kVA power facility capacity is the electrical supply demand figure for system design. Cable sizing, circuit protection, panel thermal management, and regenerative energy handling all scale from this number. The MR-J2 or MR-J2S-700 amplifier manages regeneration from the DC bus — the energy returned when a 32 kg motor decelerating a high-inertia load feeds current back into the bus. For axes with frequent high-inertia deceleration from high speed, regenerative resistor sizing is a system design item, not an afterthought.

Straight Shaft at 7kW: Coupling Engineering Matters

At 33.4 Nm continuous and 100 Nm peak, the shaft coupling interface on the HC-SF702 requires careful selection and installation. The straight shaft accepts friction-clamp or split-clamp hubs — the clamp force between hub bore and shaft OD is the sole mechanical means of torque transmission, and that force must be sufficient to carry the peak torque under the worst operating condition.

That worst condition is typically not steady-state cutting. It is sudden reversal during active machining, or emergency deceleration from maximum rapid traverse speed. At 100 Nm, a hub that is marginal at the continuous torque rating will slip. Slip on a 7kW servo axis means lost position, and on a CNC machine lost position means scrapped parts at best and axis collision at worst.

The coupling selection process starts with the peak torque — 100 Nm — and works backward through the coupling's rated transmittable torque, applying the coupling manufacturer's service factor for the motion profile (reversing service, shock loading). The safety margin should be generous at this capacity level. Hub bore tolerance, shaft OD finish, and clamping fastener torque all contribute to the final clamped joint; any of these being substandard undermines the calculation.

Mitsubishi's installation guidance for straight-shaft motors is consistent across the HC-SF range: use the shaft-end threaded hole to draw the hub axially onto the shaft rather than pressing or hammering it on. At this frame size and motor weight, impact loads during assembly are transmitted through the shaft directly to the encoder disc and bearing assembly. The encoder damage that results may not cause an immediate fault, but it produces intermittent position errors and encoder alarms that appear only under vibration — often well after commissioning, and difficult to diagnose.

For applications where a positive key connection is preferred, the HC-SF702K (keyed shaft, no brake) is the parallel variant. Both mount identically on the 176 × 176 mm flange.

J2 Generation Encoder and Amplifier Compatibility

The HC-SF702 uses the J2 platform's 14-bit serial absolute encoder at 16,384 positions per revolution. This is a serial absolute device — position data is transmitted as a serial digital signal to the amplifier, not as analog sine/cosine pairs. Battery backup in the amplifier retains the multi-turn absolute position counter between power cycles. On power-up, the amplifier reads the current absolute position and reports it to the CNC or motion controller; no reference return is required as long as the battery is healthy.

The A6BAT lithium cell lives in the servo amplifier, not in the motor. Battery replacement is performed at the amplifier during planned maintenance, independent of the motor. Monitor the amplifier's battery alarm and replace the A6BAT before full depletion — depleting the battery entirely means the absolute position counter is lost and the machine requires a homing cycle before production can resume.

Amplifier compatibility is the HC-SF702's practical advantage over the HC-SFS702 in machines running older hardware. Because the 14-bit J2 encoder predates the J2S serial protocol, it is readable by both amplifier generations:

• MR-J2-700A / MR-J2-700B — Original J2-generation amplifiers (analog/pulse and SSCNET variants). Full compatibility, no restrictions.
• MR-J2S-700A / MR-J2S-700B / MR-J2S-700CP — J2-Super amplifiers, backward-compatible with the J2 encoder. No conversion required.

The HC-SFS702 (17-bit J2S encoder) does not run on MR-J2 amplifiers. The HC-SF702 runs on both. For maintenance and engineering teams supporting machines with first-generation MR-J2-700 amplifiers, this matters: the HC-SF702 is the exact sourcing target, and no amplifier upgrade is needed to accept it.

HC-SF702 vs HC-SFS702: Which Motor Does Your Machine Need?

This question comes up every time a 7kW J2-family motor requires replacement. Both motors look nearly identical and share the same 176 × 176 mm flange, so the physical swap at the mounting face is straightforward. The encoder — and therefore the amplifier requirement — is where they diverge.

The mechanical output performance is identical. The feedback resolution and amplifier requirement are different. Verify the amplifier model currently installed in the machine before sourcing the motor. If it shows MR-J2-700 (without the S), source the HC-SF702. If it shows MR-J2S-700, either motor works — though the HC-SFS702 with its 17-bit encoder is the higher-resolution choice when the amplifier supports it.

Brake vs No Brake: Why HC-SF702 vs HC-SF702B

The HC-SF702 carries no electromagnetic brake. The HC-SF702B adds a spring-applied brake to the same motor. Beyond that single difference, the two models are identical in rated output, torque, encoder, shaft type, and amplifier compatibility.

The no-brake HC-SF702 is the correct specification when:

• The axis is horizontal, with no gravitational load component in the direction of motion
• The amplifier servo lock is adequate for holding position during any stop state in the application
• Machine safety analysis confirms that loss of servo power on this axis produces no hazardous uncontrolled movement
• The motion profile involves frequent rapid cycling where brake engagement/disengagement sequencing would add unnecessary control complexity

When any of these conditions is not met — particularly vertical axes, heavily unbalanced horizontal loads, or any axis in a machine where loss of position on servo-off is a safety concern — the HC-SF702B is the correct variant. The brake is not a convenience feature; it is a fail-safe device, and its presence or absence on a heavy-capacity motor is a safety engineering decision, not a cost optimisation.

Typical Applications

VMC X and Y feed axes. On large-format vertical machining centres, the primary X and Y table axes carry heavy workpieces and must generate sustained cutting force while maintaining precise contouring velocity. Neither axis is typically gravity-loaded in the direction of travel, making the no-brake HC-SF702 the clean specification — full 7kW capacity without the wiring and sequencing overhead of a brake system.

HMC spindle feed and quill axes. Horizontal machining centre B-axis table rotation and quill traverse axes with high-mass spindle assemblies need maximum capacity in the 2,000 rpm range. The HC-SF702's 100 Nm peak handles the inertial demands of rapid B-axis indexing and quill acceleration without oversizing the drive system.

Large CNC lathe feed axes. Heavy-duty CNC turning centres with Z-axis carriage masses that require sustained feed forces during deep turning operations use 7kW servo drives to maintain constant cutting velocity against the cutting resistance. The 2,000 rpm rated speed combined with 33.4 Nm continuous provides the drive authority these operations require.

Servo-driven rotary transfer machines. Rotary transfer lines for high-volume machining use servo drives on the primary dial indexing axis to achieve fast, precise angular positioning. The 100 Nm peak torque handles the angular acceleration demand of a large, loaded dial; the 33.4 Nm continuous rating covers the sustained torque during the cutting operations if the motor drives through a gear stage.

Mould platen drives on injection moulding machines. Servo-driven hydraulic pump replacement systems on large injection moulding machines use high-capacity servo motors directly coupled to pump shafts. The straight shaft and high continuous torque of the HC-SF702 suit this directly coupled pump drive application, where the motor runs at sustained load for extended periods and the no-brake design simplifies the installation.

New In Box, Factory Sealed

Factory sealed means original Mitsubishi packaging — outer carton, inner foam support, and protective covers all undisturbed. Shaft-end cap in place, encoder and power connector ports covered, no prior installation. At approximately 32 kg, the HC-SF702 ships in robust packaging that protects the oil seal, encoder assembly, and shaft through transit.

For a machine currently down awaiting this motor, in-stock new-in-box eliminates repair turnaround entirely. No reconditioning variables, no questions about previous service history, no uncertainty about encoder condition after a prior failure event. The motor arrives in the same state it left the Mitsubishi factory.

For long-term storage, cool, dry, vibration-free conditions maintain full specification over several years. Beyond five years in storage, a brief pre-commissioning slow shaft rotation redistributes bearing grease before the motor enters service.

Frequently Asked Questions

Q1: Which amplifiers are compatible with the HC-SF702?

The HC-SF702 is compatible with both the original J2-generation and J2-Super amplifiers at the 700 class. Confirmed compatible models are the MR-J2-700A and MR-J2-700B (original J2 generation), and the MR-J2S-700A, MR-J2S-700B, and MR-J2S-700CP (J2-Super generation). The 14-bit J2 encoder is readable by both amplifier generations. The HC-SF702 is not compatible with MR-J3 or MR-J4 amplifiers, which use an entirely different encoder interface.

Q2: What is the difference between the HC-SF702 and the HC-SFS702?

Both are 7kW, 2,000 rpm, 33.4 Nm, straight shaft, no brake motors on a 176 × 176 mm flange — mechanically interchangeable at the mount. The difference is the encoder generation: the HC-SF702 uses a 14-bit encoder (16,384 ppr) and works with both MR-J2 and MR-J2S amplifiers. The HC-SFS702 uses a 17-bit encoder (131,072 ppr) and requires MR-J2S amplifiers only. If the machine runs original MR-J2-700 amplifiers, source the HC-SF702. If it runs MR-J2S-700 amplifiers, either motor works — the HC-SFS702 offers higher resolution feedback.

Q3: Why is there no electromagnetic brake on the HC-SF702?

The HC-SF702 is the no-brake variant in the 7kW J2 straight-shaft range by design — intended for horizontal axes and any drive where mechanical fail-safe hold is not required. Position at rest is maintained through amplifier servo lock. For applications needing fail-safe mechanical hold — vertical axes, gravity-loaded mechanisms, or any axis where servo-off causes hazardous uncontrolled movement — the HC-SF702B (identical motor with spring-applied electromagnetic brake) is the correct specification.

Q4: Does the absolute encoder need a battery, and where is it located?

Yes. The 14-bit serial absolute encoder retains multi-turn position data through power-off using a Mitsubishi A6BAT lithium battery housed inside the servo amplifier — not in the motor. A healthy battery keeps absolute position through any power interruption, eliminating the need for a homing cycle on restart. Replace the A6BAT when the amplifier displays a low-battery warning. Allowing full battery depletion causes loss of stored absolute position, requiring a reference return cycle before the machine can resume production.

Q5: The HC-SF702 weighs approximately 32 kg — what should I know about handling and installation?

At 32 kg, the HC-SF702 requires two people or a mechanical assist for safe positioning during installation. Use the motor's M8 suspension bolt hole (on the front face near the flange) for rigging if lifting from above — do not lift by the cables, connector, or shaft. When aligning the motor to the ballscrew or coupling, use alignment tools to minimise both angular and parallel offset before tightening the mounting bolts; radial shaft loads from a misaligned coupling at this frame size can reduce bearing life significantly. Never hammer any component onto the shaft — use the shaft-end threaded hole and a drawbolt to fit hubs.