The HG-SR73 is Mitsubishi Electric’s 750 W low-inertia medium-capacity servo motor from the HG-SR series for the MELSERVO-J4 and MELSERVO-J3 servo amplifier platforms, providing 2.39 N·m rated torque at 3,000 rpm with a 22-bit multi-turn absolute encoder as standard — the mid-range model in the lower HG-SR power classes, designed for primary CNC machining centre feed axes, medium-payload robot primary axes, and conveyor positioning drives where 750 W of continuous servo power represents the standard specification for a broad range of industrial machine axis requirements. Atlantech Drives holds stock of the HG-SR73. Contact us for fast worldwide delivery and competitive pricing.
What Is the HG-SR73?
The HG-SR73 is a Mitsubishi Electric MELSERVO HG-SR series servo motor providing 750 W (0.75 kW) continuous rated output at 3,000 rpm rated speed, with a peak torque of 7.16 N·m (3× rated torque). Compatible with MR-J4-70A (pulse train input) and MR-J4-70B (SSCNET III/H network) servo amplifiers, the HG-SR73 is the standard motor pairing for 750 W servo axes in MELSERVO-J4 systems. The rotor inertia of 0.410 × 10⁻⁴ kg·m² is higher than the 400 W HG-SR43 (0.148 × 10⁻⁴ kg·m²) but remains within the low-inertia HG-SR series classification — the motor responds well to rapid position changes while providing adequate rotor mass to smooth velocity fluctuations in applications with varying load torque. The 22-bit absolute encoder provides 262,144 pulses/rev resolution with multi-turn absolute position retention, maintained across power cycles by the MR-BAT6V1SET battery in the servo amplifier. In J3 motor compatibility mode, the HG-SR73 is compatible with MR-J3-70A and MR-J3-70B amplifiers (parameter PA22 = 1), enabling direct replacement of legacy HC-SFS72 or HC-RFS73 motors in existing J3-era multi-axis servo systems.
Key Technical Specifications
- Model: HG-SR73
- Rated Output Power: 750 W (0.75 kW)
- Rated Torque: 2.39 N·m
- Rated Speed: 3,000 rpm
- Maximum Speed: 5,000 rpm
- Peak Torque: 7.16 N·m (3× rated)
- Rotor Inertia: 0.410 × 10⁻⁴ kg·m²
- Encoder: 22-bit multi-turn absolute (262,144 pulses/rev)
- Power Supply Voltage: 200 VAC (via compatible servo amplifier)
- Insulation Class: F (155°C maximum winding temperature)
- Protection Rating: IP65 (shaft seal and connector side)
- Mounting: Square flange, IEC standard
- Operating Temperature: 0°C to 40°C (ambient)
- Weight: Approx. 2.1 kg
Architecture & Design Overview
The HG-SR73 implements the permanent magnet synchronous motor (PMSM) design used across the entire HG-SR series — neodymium iron boron (NdFeB) rare-earth permanent magnets on the rotor provide high flux density enabling the motor’s high torque density relative to frame size, while the stator’s distributed winding design minimises torque ripple for smooth velocity control at low speeds. The 22-bit absolute encoder is integrated into the motor’s rear end-bell as a compact module that communicates with the servo amplifier via Mitsubishi’s proprietary serial encoder interface at each servo control cycle, providing the current position feedback required by the position and speed loops. The motor’s thermal management relies on natural convection from the motor body surface — the frame fins increase the surface area for heat dissipation, and the continuous rated torque specification (2.39 N·m) is the maximum torque sustainable indefinitely without exceeding the F-class insulation temperature limit at 40°C ambient. The HG-SR73’s IP65 protection is achieved by the shaft seal at the front end-bell (preventing water and dust ingress along the shaft) and the IP65-rated motor power and encoder connectors — the connector ratings apply only when the mating cable connectors are fully engaged, as partially mated connectors bypass the IP65 sealing. The motor’s square mounting flange follows the IEC standard face configuration, with the shaft centre height and mounting bolt pattern dimensionally compatible with DIN V 42955 / ISO 9283 standard servo motor mounting interfaces — enabling use of standard servo motor couplings, gearboxes, and mounting adaptors designed for IEC-standard servo motors.
Expert Tips
When commissioning an HG-SR73 with an MR-J4-70A or MR-J4-70B servo amplifier in a new machine axis, select the servo response level in MR Configurator2’s auto-tuning setup based on the mechanical system’s stiffness — for rigid direct-coupled ball screw drives with low backlash, response level 8–12 is typically achievable; for belt drives or gearbox-coupled systems with compliance, start at level 4–6 and increase cautiously. At 750 W with 2.39 N·m rated torque, the HG-SR73 has sufficient torque to excite mechanical resonances in compliance-containing drive trains — if the auto-tuning result produces audible resonance (a high-pitched ringing or vibration during motor deceleration), use MR Configurator2’s machine analyser to identify the resonance frequency and set the AVSC II notch filter to suppress it before increasing the servo response level further. For the HG-SR73 installed on a vertical axis without a mechanical brake, verify the servo system’s ability to hold position under gravity loading when the servo enable is asserted but no motion command is active — the servo holding torque must exceed the gravitational load torque at all axis positions to prevent creep. If gravitational holding is marginal, add the HG-SR73B brake variant or install an external fail-safe brake on the axis — do not rely on the servo’s holding capability alone for vertical axes carrying significant loads. When routing the HG-SR73’s motor power cable (U, V, W phases) in the machine panel, maintain at least 150 mm separation from the encoder cable to prevent motor switching noise from coupling into the 22-bit encoder signal — at 262,144 pulses/rev, even a single missed or false encoder count during servo operation causes a position error that the servo control loop corrects with an abrupt velocity spike, visible as a position disturbance in the servo waveform monitor.
Frequently Asked Questions
Q: What is the difference in maximum speed between the HG-SR73 (5,000 rpm) and the HG-SR43 (6,000 rpm)?
A: The HG-SR73’s maximum rated speed is 5,000 rpm versus 6,000 rpm for the HG-SR43 — a consequence of the larger rotor diameter and mass of the 750 W frame, which increases centrifugal stress on the rotor magnets and limits the maximum safe mechanical speed. For applications requiring the full 6,000 rpm speed capability at 750 W power level, Mitsubishi’s HG-SR72 (750 W, 2,000 rpm rated speed) variant or the HG-RR series (high-speed, high-inertia motors rated above 3,000 rpm) should be evaluated. For most CNC machining centre rapid traverse applications, 5,000 rpm maximum is adequate at 750 W.
Q: Can the HG-SR73 be connected directly to the motor shaft without a coupling, using a rigid flange connection to the load?
A: Direct rigid flange connection (without a coupling) between the HG-SR73 shaft and the load mechanism is only acceptable if the alignment between the motor shaft and the load shaft is within the motor manufacturer’s specified misalignment tolerance — typically ±0.05 mm radial and ±0.1° angular. Misalignment beyond these limits generates bearing radial loads that reduce bearing life and can cause encoder output shaft vibration affecting position measurement accuracy. In practice, a flexible jaw coupling (Oldham or spider type) is recommended for all HG-SR73 direct-drive axis connections to accommodate the inevitable small misalignment present in real mechanical assemblies.
Q: Is the HG-SR73 available with a Food & Beverage (F&B) rated version for hygienic applications?
A: The standard HG-SR73 carries IP65 protection suitable for incidental water exposure. For food and beverage applications requiring regular washdown, Mitsubishi offers stainless steel shaft and special sealing options on selected HG-SR series motors — consult Mitsubishi’s servo motor options catalogue or Atlantech Drives’ technical team for the specific F&B variant availability for the HG-SR73 frame size.
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