Mitsubishi HF-SP81MK-S12 | MELSERVO-J3 Series AC Servo Motor
850W, Keyed Shaft, Brake, IP66 - Genuine New
Product Overview
The Mitsubishi HF-SP81MK-S12 is an 850W AC servo motor from Mitsubishi Electric's MELSERVO-J3 series. This mid-frame, medium-inertia servo motor is designed for demanding feed axis and positioning requirements in CNC machine tools and industrial automation equipment.
This variant combines a keyed shaft, integrated holding brake, and IP66 environmental sealing - addressing mechanical coupling integrity, fail-safe position holding, and protection against industrial contamination simultaneously.
Rated at 8.12 Nm continuous torque with 1,000 RPM rated speed, this is a low-speed, high-torque motor built to sustain force output. It operates from a 200VAC class supply and features an 18-bit absolute encoder delivering over 260,000 counts per revolution for precise positioning.
Key Specifications
| Parameter |
Value |
| Rated Output |
850 W (0.85 kW) |
| Rated Torque |
8.12 Nm |
| Rated Current |
4.5 A |
| Supply Voltage |
200VAC Class |
| Rated Speed |
1,000 RPM |
| Encoder |
18-Bit Absolute (built-in) |
| Shaft Configuration |
Keyed Straight Shaft |
| Holding Brake |
Integrated |
| Ingress Protection |
IP66 |
| Flange Size |
130 × 130 mm |
| Series |
MELSERVO-J3 - HF-SP Type |
| Weight |
5.44 kg (11.99 lbs) |
| Manufacturer Status |
Discontinued |
HF-SP Series - Medium Inertia, High Torque
The HF-SP motor type within the MELSERVO-J3 family is designed for applications with moderate to high reflected load inertia where sustained torque is prioritized over high-speed dynamic response.
At 1,000 RPM rated speed, the HF-SP81 produces 8.12 Nm torque, well-matched to direct ballscrew coupling on machines with moderate lead pitch values. This generates substantial linear thrust force without requiring additional gearing.
For heavy axis saddles, large worktables, and drives requiring minimal position deviation under load, the HF-SP's torque density and inertia matching characteristics provide the axis stiffness that precision machining demands.
18-Bit Absolute Encoder
Every HF-SP series motor includes a built-in 18-bit absolute encoder as standard - providing 262,144 unique position counts per shaft revolution without requiring homing cycles at startup.
This eliminates non-productive time savings from homing routines and prevents positioning errors that incremental encoder systems are susceptible to during power quality issues or unexpected E-stops.
The high resolution supports smooth interpolation at low speeds, directly influencing surface finish quality on multi-axis contouring work and positioning accuracy in high-cycle applications.
Keyed Shaft Design
The keyed shaft provides positive mechanical drive connection between the motor shaft and mating coupling hub or pulley, preventing rotational slip under shock loads, sustained high-torque demand, and repeated direction reversals.
For medium-inertia CNC feed axes involving continuous bidirectional positioning and periodic heavy cuts, the keyed shaft is the appropriate specification for reliable torque transmission.
Integrated Holding Brake & IP66 Protection
The holding brake operates on fail-safe principles: spring-applied when de-energized, electrically released during normal operation. On power loss, emergency stop, or servo alarm, the brake engages automatically to hold the shaft position.
IP66 protection means the motor housing is fully sealed against dust and protected against powerful water jets from any direction - appropriate for machine tool environments with active coolant systems and high-pressure cleaning routines.
Drive Compatibility - MELSERVO-J3
The HF-SP81MK-S12 is paired with Mitsubishi's MR-J3 series servo amplifier. The appropriate drive selection accounts for the motor's 850W output and 4.5A rated current - typically the MR-J3-70B or MR-J3-100B amplifier class.
Communication interfaces include SSCNET III for high-speed fibre-optic network connection in multi-axis systems, plus analogue and pulse-train command modes for standalone applications.
Frequently Asked Questions
What servo drive is compatible with the HF-SP81MK-S12?
This motor is designed for use with Mitsubishi MR-J3 series servo amplifiers - specifically the MR-J3-70B or MR-J3-100B for the 850W motor class. The J3 drive natively supports the HF-SP motor type and 18-bit absolute encoder interface.
The motor is discontinued - can it be replaced with a current Mitsubishi model?
Yes, but not as a direct plug-and-play swap. Equivalent current-generation motors may share similar torque class but differ in flange dimensions, shaft size, connector pinouts, and drive compatibility. Sourcing a refurbished HF-SP81MK-S12 typically involves less risk and downtime than cross-generation substitution.
What does IP66 protection mean for this motor in a machining environment?
IP66 means the motor is fully dust-tight and protected against high-pressure water jets from any direction. This covers direct coolant spray, wash-down cleaning, and sustained fluid exposure in cutting zones without ingress into the motor housing.
Why does this motor have a rated speed of only 1,000 RPM?
The HF-SP type is a medium-inertia, high-torque motor optimized for sustained force output at moderate speeds. A 1,000 RPM rated speed is appropriate for direct-coupled ballscrew drives where rapid traverse and cutting feedrate requirements are met within this rotational range.
What inspection steps are most important for a used HF-SP81MK-S12?
Test the brake first - apply and release supply voltage while confirming positive shaft lock and clean release. Measure three-phase winding resistance for balance and insulation resistance to earth. Inspect the 18-bit encoder connector for corrosion or damage, and verify bearing condition by rotating the shaft manually.
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