The MR-J4-350B is Mitsubishi Electric’s 3.5 kW MELSERVO-J4 series servo amplifier for 200 V single-phase or three-phase AC power supply with SSCNET III/H optical fibre network interface — providing closed-loop servo control at continuous rated output current of 17.0 A for Mitsubishi HG-SR and HG-RR series 3.5 kW servo motors, filling the gap between 2 kW and 5 kW in the MR-J4-B SSCNET III/H sub-series for applications where 2 kW is insufficient and 5 kW would be oversized for the mechanical load. The MR-J4-350B is available through Atlantech Drives — quote within 24-48 hours, worldwide express shipping, 12-month warranty.
What Is the MR-J4-350B?
The MR-J4-350B is a MELSERVO-J4 series servo amplifier providing 3.5 kW (3,500 W) continuous output power via SSCNET III/H, compatible with Mitsubishi HG-SR352, HG-SR3524, HG-RR353, and equivalent 3.5 kW servo motors with 22-bit multi-turn absolute encoders. The MR-J4-350B occupies the critical mid-range power position in the MR-J4-B sub-series, enabling right-sizing of servo axes in applications where the load torque at rated speed falls between 2 kW and 5 kW — specifying the MR-J4-350B instead of the MR-J4-500B reduces motor frame size, amplifier size, and system cost while meeting the application’s power requirement without oversizing. The housing width increases to 85 mm compared to the MR-J4-200B’s 70 mm, reflecting the higher power dissipation requirements of the 3.5 kW power stage. All MR-J4-B standard features are included: SSCNET III/H command at 0.888 ms or 0.444 ms cycle, 22-bit absolute encoder support, AVSC II resonance suppression, dual encoder fully closed-loop support, and dual-channel STO safety function compliant with IEC 61800-5-2 SIL2.
Key Technical Specifications
- Model: MR-J4-350B
- Rated Output Power: 3.5 kW (3,500 W)
- Power Supply: 200–240 VAC single-phase or three-phase, 50/60 Hz
- Continuous Output Current: 17.0 A
- Maximum Output Current: 51.0 A (3× continuous peak)
- Compatible Servo Motors: HG-SR352, HG-SR3524, HG-RR353, HG-RR3534 and equivalent
- Command Interface: SSCNET III/H optical fibre (150 Mbps full-duplex)
- Communication Cycle: 0.444 ms or 0.888 ms (selectable)
- Encoder Interface: Serial 22-bit absolute encoder (262,144 pulses/rev)
- Safety Function: STO (Safe Torque Off), IEC 61800-5-2 SIL2 / EN ISO 13849-1 PLe
- Regenerative Brake: Built-in, external MR-RB series resistor connectable
- Housing Width: 85 mm
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 85 mm × 200 mm × 192 mm
- Weight: Approx. 2.8 kg
Architecture & Design Overview
The MR-J4-350B implements the same three-loop digital servo control architecture — position loop, speed loop, and current loop at 3.5 kHz bandwidth — as all MR-J4-B variants, with the power stage scaled for 3.5 kW continuous output. The amplifier’s SSCNET III/H communication processor handles all network communication independently of the servo control processor, ensuring that SSCNET III/H network load or communication anomalies do not affect the servo control loop’s deterministic execution. The Advanced Vibration Suppression Control II implementation in the MR-J4-350B includes the machine resonance analyser function accessible via MR Configurator2 — connecting MR Configurator2 via USB and running the machine analyser sweeps the servo system across a frequency range and plots the frequency response, identifying resonance peaks that should be suppressed by the notch filters. At 3.5 kW with a medium-frame HG-SR352 motor, mechanical resonance frequencies typically fall in the 100–500 Hz range for ball screw driven axes with flexible couplings, and the AVSC II notch filters effectively suppress these resonances to prevent oscillation at higher servo gain settings. The MR-J4-350B’s adaptive filter function continuously monitors the servo system’s vibration signature during normal operation and adjusts the notch filter frequencies in real time if the resonance frequency drifts due to thermal expansion, mechanical wear, or load changes — eliminating the need to retune the notch filters at each maintenance interval for applications with variable load conditions.
Expert Tips
When specifying the MR-J4-350B for a new machine axis, use Mitsubishi’s servo sizing software (MRZJW3-MOTSZ111E or the online Servo Selection Tool) to verify that the 3.5 kW motor’s continuous torque at the required speed does not exceed the motor’s rated continuous torque at the application’s duty cycle — a motor that is thermally adequate for the application’s RMS torque demand at rated speed, but not oversized, minimises motor inertia and improves servo response bandwidth. For axes with high inertia loads (rotary tables, large gantry carriages), calculate the load inertia ratio and verify it is within the MR-J4-350B’s recommended range — high inertia ratios above 30:1 at the motor shaft require careful servo tuning and AVSC II to prevent mechanical oscillation. The MR-J4-350B’s one-touch auto-tuning function determines the load inertia ratio automatically during the tuning run — verify the identified inertia ratio in MR Configurator2 after tuning and confirm it matches the calculated value from the mechanical design data. A significant discrepancy (more than 50%) between calculated and identified inertia ratio indicates a mechanical transmission problem (loose coupling, excessive backlash, incorrect gear ratio setting) that should be resolved before proceeding with servo commissioning. For the MR-J4-350B’s regenerative energy management, monitor the regenerative brake usage percentage in MR Configurator2’s diagnostic display during a representative duty cycle before deciding whether an external regenerative resistor is needed — if the built-in resistor usage percentage approaches 80% during normal operation, add an external MR-RB series resistor to provide adequate regenerative capacity margin for occasional duty cycle peaks.
Frequently Asked Questions
Q: Is the MR-J4-350B suitable for driving a 3.5 kW servo motor on a vertical axis without a mechanical brake, relying on the servo holding torque?
A: Using servo holding torque alone on a vertical axis without a mechanical brake is only appropriate for light loads with short holding periods — the servo cannot maintain position if power is lost (E-stop, power failure), and the thermal load from continuous holding torque at standstill may exceed the motor’s continuous torque rating depending on the load weight and duty cycle. For vertical axes with significant gravitational load, a dedicated motor brake (spring-applied, power-released) is required for safe holding during power-off conditions. The MR-J4-350B’s STO function specifically removes drive power from the motor — activating STO on a vertical axis without a mechanical brake will cause the axis to fall under gravity.
Q: Can the MR-J4-350B’s communication cycle be changed from 0.888 ms to 0.444 ms without hardware modification?
A: Yes. The communication cycle selection (0.888 ms or 0.444 ms) is set by the motion controller’s system configuration parameter, not by a hardware setting on the MR-J4-350B. All amplifiers on the SSCNET III/H chain operate at the cycle time selected in the motion controller — changing the motion controller’s SSCNET cycle parameter from 0.888 ms to 0.444 ms changes all amplifiers in the chain simultaneously. Verify that the motion controller supports 0.444 ms operation (not all motion controllers support this high-speed mode) before selecting it.
Q: Does the MR-J4-350B support the SSCNET III/H communication redundancy function for high-availability applications?
A: The standard MR-J4-350B supports the standard SSCNET III/H daisy-chain topology without hardware redundancy — a single fibre fault between two amplifiers in the chain interrupts communication to all downstream amplifiers. For high-availability applications requiring communication redundancy, the SSCNET III/H ring topology (where the chain end connects back to the controller) provides automatic loop-back on single cable fault, maintaining communication to all amplifiers within approximately 0.5 seconds of fault detection. Verify the specific motion controller’s support for SSCNET III/H ring topology before specifying this configuration.
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