The HG-MR73 is a 750 W low-inertia AC servo motor from Mitsubishi Electric’s MELSERVO-J4 series, designed for high-speed positioning applications where rapid acceleration and deceleration are critical — including pick-and-place machines, semiconductor handling equipment, small-scale robotics, and high-throughput packaging lines. The «HG-MR» designation identifies the low-inertia rotor construction optimised for dynamic response, while «73» denotes the 750 W rated output at 3000 rpm rated speed. The motor ships with a 22-bit absolute/incremental serial encoder (4,194,304 pulses/revolution) enabling precise positioning without a separate battery-backed reference. The HG-MR73 is available through Atlantech Drives — quote within 24-48 hours, worldwide express shipping, 12-month warranty.
What Is the HG-MR73?
The HG-MR73 is part of Mitsubishi’s fourth-generation MELSERVO-J4 platform, launched to pair with the MR-J4 series servo amplifiers over the SSCNET III/H high-speed fibre-optic servo network. Within the HG-MR low-inertia family — which spans 50 W (HG-MR053) through 750 W (HG-MR73) — this model sits at the top of the low-inertia power range; above 750 W, Mitsubishi transitions users to the HG-SR medium-inertia family for applications requiring higher torque capacity. The low-inertia rotor design delivers exceptional acceleration performance: the HG-MR73 achieves a rotor inertia of 1.43×10⁻⁴ kg·m², allowing machine designers to achieve very short positioning cycle times when the load-to-motor inertia ratio is kept within recommended limits (typically 15:1 or lower for optimum tuning stability). The standard shaft is straight with key; oil-seal and keyless variants are available as suffix options. The HG-MR73 is supplied without a holding brake as standard; the brake-equipped equivalent is the HG-MR73B.
Key Technical Specifications
- Rated Output: 750 W
- Rated Speed: 3000 rpm
- Maximum Speed: 6000 rpm
- Rated Torque: 2.39 N·m
- Maximum Torque: 8.36 N·m (350% of rated)
- Rated Current: 5.1 A
- Rotor Inertia: 1.43×10⁻⁴ kg·m² (without brake)
- Encoder: 22-bit absolute/incremental serial encoder (4,194,304 pulses/rev)
- Insulation Class: F
- Protection Rating: IP65 (shaft-through portion excluded)
- Compatible Amplifier: MR-J4-70A / MR-J4-70B / MR-J4-70GF
- Operating Ambient: 0 °C to +40 °C, 80% RH max (non-condensing)
- Shaft Configuration: Straight shaft with key (standard)
- Weight: Approx. 3.1 kg
Compatibility & System Integration
The HG-MR73 pairs with the MR-J4-70A (analog/pulse control), MR-J4-70B (SSCNET III/H fibre-optic network), or MR-J4-70GF (CC-Link IE TSN) servo amplifier depending on the chosen control architecture. The 22-bit serial encoder communicates with the amplifier via a dedicated encoder cable (MR-J3ENCBL_M-A1-L for straight, or MR-J3ENCBL_M-A2-L for right-angle connector) — these cables are not interchangeable with older MR-J2S encoder cables despite the similar connector appearance. For multi-axis synchronised motion applications, the HG-MR73 integrates seamlessly into MELSEC iQ-R motion controller systems (RD77MS, RD77GF modules) via SSCNET III/H with sub-microsecond synchronisation across all axes. When replacing legacy MR-J3 systems using the earlier HF-MP73 motor, note that the HG-MR73 is electrically and mechanically compatible with MR-J3-70A/B amplifiers in most cases, but Mitsubishi recommends upgrading to MR-J4 to access the improved auto-tuning algorithms and machine resonance suppression features.
Installation Advice
Installation tip: the HG-MR73’s low-inertia rotor makes it particularly sensitive to excessive load-to-motor inertia mismatch. Calculate the reflected load inertia at the motor shaft before commissioning and target a ratio below 10:1 for optimum positioning performance — ratios above 15:1 typically require manual gain tuning and may exhibit audible resonance at mid-frequency. For belt-driven loads, ensure the belt tension is within the belt manufacturer’s specification: excessive tension increases radial shaft load and shortens bearing life, while insufficient tension causes belt slip that corrupts the encoder’s load-side position estimate used by the MR-J4’s adaptive vibration suppression. Mount the motor with the connector box oriented downward or to the side to prevent cable strain and water ingress in washdown environments. When using the motor on a vertical axis, always specify the HG-MR73B variant with holding brake — the standard HG-MR73 has no mechanical brake and will allow the load to fall on power loss.
Frequently Asked Questions
Q: Can the HG-MR73 be used as a direct replacement for the HF-MP73 from the MR-J3 generation?
A: Mechanically and electrically the HG-MR73 is compatible with MR-J3-70A/B amplifiers in most installations, but the encoder protocol differs: HF-MP73 uses an 18-bit encoder while HG-MR73 uses 22-bit. The MR-J3 amplifier firmware will recognise the higher-resolution encoder automatically, but to access MR-J4’s advanced features (adaptive filter, vibration suppression 2, auto-tuning mode 3) you must also upgrade the amplifier to MR-J4-70A/B.
Q: What is the difference between HG-MR73 and HG-KR73?
A: Both are 750 W MELSERVO-J4 motors but with different inertia ratings for different applications. HG-MR73 is low-inertia (1.43×10⁻⁴ kg·m²) for high-speed, high-acceleration applications with low load inertia. HG-KR73 is ultra-low-inertia (0.87×10⁻⁴ kg·m²) for even higher acceleration but with tighter load inertia matching requirements. Choose HG-MR for general high-speed positioning; choose HG-KR for rotary indexing or cam profiling where cycle time is critical.
Q: Does the HG-MR73 require a battery for absolute position retention?
A: Yes, for absolute position mode. The 22-bit encoder operates in either incremental or absolute mode; absolute mode requires a battery (MR-BAT6V1SET) connected to the amplifier (not the motor) to retain multi-turn position data during power-off. Without the battery, the system operates in incremental mode and requires a homing sequence on each power cycle.
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