The MR-J4-20B is Mitsubishi Electric’s 200 W 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 1.5 A for Mitsubishi HG-KR and HG-MR series small-frame servo motors, doubling the continuous output power of the MR-J4-10B for 200 W axis requirements in multi-axis electronic assembly, medical device manufacturing, and precision inspection equipment. Atlantech Drives holds stock of the MR-J4-20B. Contact us for fast worldwide delivery and competitive pricing.
What Is the MR-J4-20B?
The MR-J4-20B is a MELSERVO-J4 series servo amplifier providing 200 W (0.2 kW) continuous output power via SSCNET III/H optical fibre, receiving all position commands from a compatible MELSEC motion controller at 0.888 ms or 0.444 ms communication cycle time. Like all MR-J4-B series amplifiers, the MR-J4-20B has no pulse train input — position, speed, and torque commands are delivered exclusively via the SSCNET III/H optical fibre link, ensuring deterministic command delivery independent of host controller scan time variation. The MR-J4-20B is compatible with Mitsubishi HG-KR23, HG-MR23, and equivalent 200 W servo motors equipped with the standard 22-bit multi-turn absolute encoder, providing absolute position feedback at 262,144 pulses per revolution without requiring battery replacement beyond the amplifier’s battery cycle — the MR-J4’s absolute encoder battery (MR-BAT6V1SET) is installed in the amplifier, not in the motor, simplifying motor field replacement. The MR-J4-20B shares the same 40 mm compact housing width as the MR-J4-10B, enabling dense axis packing in multi-axis panels where multiple servo axes must fit within a constrained panel width.
Key Technical Specifications
- Model: MR-J4-20B
- Rated Output Power: 200 W (0.2 kW)
- Power Supply: 200–240 VAC single-phase or three-phase, 50/60 Hz
- Continuous Output Current: 1.5 A
- Maximum Output Current: 4.5 A (3× continuous peak)
- Compatible Servo Motors: HG-KR23, HG-MR23, HG-KR053B, HG-MR053B 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
- Regenerative Brake: Built-in
- Housing Width: 40 mm
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 40 mm × 150 mm × 138 mm
- Weight: Approx. 0.8 kg
Architecture & Design Overview
The MR-J4-20B implements the same three-loop digital servo control architecture as all MR-J4-B variants — position loop, speed loop, and current loop — with the position command arriving via SSCNET III/H at each communication cycle rather than from pulse train input. The motion controller transmits the next position setpoint (in encoder units) to the MR-J4-20B at every 0.888 ms or 0.444 ms communication cycle, and the amplifier’s internal position loop calculates the position error and generates the corresponding speed command for the speed loop. This command structure — where the motion controller provides absolute position setpoints each cycle rather than incremental pulses — enables the motion controller to implement coordinated multi-axis interpolation (linear, circular, helical) with sub-millisecond update rates that are not achievable with pulse train systems where the command update rate is limited by the PLC scan time. The MR-J4-20B’s current loop bandwidth is 3.5 kHz, identical across all MR-J4-B variants regardless of power rating — the torque response speed is the same for 200 W and 22,000 W amplifiers, ensuring consistent servo behaviour across mixed-power multi-axis systems. The Advanced Vibration Suppression Control II function in the MR-J4-20B implements two independently tunable notch filters for machine resonance suppression, with automated resonance frequency identification available via MR Configurator2’s machine analyser function — this capability is particularly valuable for 200 W axes driving lightweight, flexible mechanism structures (thin-arm pick-and-place mechanisms, scanner mirror assemblies) where mechanical resonance frequencies are within the servo bandwidth.
Troubleshooting Guide
For MR-J4-20B amplifiers generating AL.9F (SSCNET III/H communication error) after otherwise successful operation, the most common causes are POF cable degradation and connector contamination. Plastic optical fibre has a finite bend cycle life and can develop micro-cracks in the fibre core after repeated bending at the connector entry point — inspect the POF cable for sharp bends or kinks at the connector where the cable exits the amplifier, and replace cables showing cracking of the outer jacket at the bend point. If the AL.9F alarm occurs only at startup and clears after a few seconds, the amplifier’s optical receiver may be marginal due to connector contamination — clean both the CN1A and CN1B connector endfaces with a fibre cleaning tool and re-test. For MR-J4-20B amplifiers generating AL.50 (overload) during normal operation at loads within the 200 W continuous rating, verify the motor winding temperature is not contributing to the alarm — the overload alarm is triggered by the amplifier’s thermal model (based on output current history), not a direct temperature measurement, and an underestimated load inertia in the servo parameter settings causes the thermal model to accumulate thermal load faster than the actual motor. Re-run auto-tuning in MR Configurator2 with the correct load inertia ratio identified and verify the servo response level does not exceed the level at which the overload model approaches the trip threshold during the operating duty cycle.
Frequently Asked Questions
Q: Can the MR-J4-20B be used with the same SSCNET III/H chain as MR-J4-500B or MR-J4-700B higher-power amplifiers?
A: Yes. All MR-J4-B series amplifiers regardless of power rating use identical SSCNET III/H communication at the same 150 Mbps data rate and 0.888 ms (or 0.444 ms) cycle time. A single SSCNET III/H chain managed by a Q172DSCPU motion controller can simultaneously include MR-J4-10B (100 W), MR-J4-20B (200 W), MR-J4-500B (5 kW), and MR-J4-700B (7 kW) amplifiers — the motion controller manages all axes with identical command update rates regardless of each axis’s power rating.
Q: What is the difference between the 0.444 ms and 0.888 ms SSCNET III/H communication cycle on the MR-J4-20B?
A: The 0.444 ms communication cycle (half the standard 0.888 ms) provides twice as frequent position command updates, improving coordinated motion smoothness and reducing position error during high-acceleration moves. The 0.444 ms cycle is available on motion controllers supporting the high-speed SSCNET III/H mode (Q173DSCPU, RD77MS with specific firmware). For most standard multi-axis machine applications, the 0.888 ms cycle provides adequate synchronisation; for high-speed, high-precision applications such as semiconductor wafer handling and precision optical scanning, the 0.444 ms cycle reduces position following error at high speeds.
Q: Does the MR-J4-20B’s built-in regenerative resistor handle all standard small-motor applications, or is an external resistor needed?
A: The MR-J4-20B’s built-in regenerative resistor handles the regenerative energy from 200 W motor decelerations in most standard applications. The built-in resistor continuous power rating (approximately 10 W) is sufficient for light-duty axes with infrequent deceleration cycles. For applications with high deceleration frequency (multiple decelerations per second) or high load inertia, calculate the average regenerative power and compare against the 10 W built-in limit — if the calculated power exceeds 10 W, an external MR-RB series regenerative resistor must be connected to the MR-J4-20B’s regenerative resistor terminals.
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