Mitsubishi AC Servo Migration Guide: Upgrading MR-J3 to MR-J4 (Pulse & SSCNET III/H)
1. The Operational Necessity of Migrating from MR-J3 to MR-J4
The Mitsubishi MELSERVO MR-J3 series, initially commercialized in 2004, has entered complete Discontinuation (End of Life - EOL). Procurement lead times and replacement costs for vintage stock are escalating sharply. Proactive retrofitting to the MR-J4 Series prevents catastrophic factory downtime. Technical Superiority of MR-J4: - Encoder Resolution: Upgraded from 18-bit (262,144 pulses/rev) in MR-J3 to 22-bit (4,194,304 pulses/rev) in MR-J4, yielding 16-fold precision gains. - Speed Frequency Response: Increased from 900 Hz to 2.5 kHz, drastically suppressing machine resonance and cycle latency. - SSCNET III/H Optical Bus: Triple bandwidth throughput jump from 50 Mbps to 150 Mbps for synchronized multi-axis control.
2. Cross-Reference Replacement Matrix
| Legacy Model (MR-J3) | Replacement Model (MR-J4) | Interface Type | Power Range |
|---|---|---|---|
| MR-J3-A (General Interface) | MR-J4-A (-RJ) | Pulse Train / Analog Voltage | 100W to 22 kW |
| MR-J3-B (SSCNET III) | MR-J4-B (-RJ) | Optical SSCNET III/H (150 Mbps) | 100W to 22 kW |
| <strong>Motor:</strong> HF-KP / HF-MP Series | <strong>Motor:</strong> HG-KR / HG-MR Series | Low Inertia Motor | 50W to 750W |
| <strong>Motor:</strong> HF-SP Series | <strong>Motor:</strong> HG-SR Series | Medium Inertia Motor | 500W to 7.0 kW |
3. Driving Legacy HF Motors with MR-J4-B-RJ020 Amplifiers
When retrofitting a damaged drive while keeping existing HF motors and installed drag chain cabling intact, deploy the dedicated MR-J4-_B-RJ020 amplifier variant. It directly decodes 18-bit feedback signals from HF-KP, HF-MP, and HF-SP motors, circumventing expensive motor replacements.
4. Parameter Conversion using MR Configurator2
- Launch MR Configurator2 and open the archived MR-J3 parameter file.
- Select Project -> Change Model from the main menu.
- Target MR-J4-A or MR-J4-B corresponding to the replacement hardware.
- The utility recalculates Electronic Gear ratios (CMX/CDV) to match the 22-bit encoder resolution scaling.
- Verify Torque Limit thresholds and Safe Torque Off (STO) assignments before flashing the new drive.
Optical Cable Handling & SSCNET Fallback
Standard MR-J3BUS_M optical patch cords are plug-compatible with SSCNET III/H ports, provided fiber bending radius limits (25-50 mm minimum) have not been violated. Connecting an MR-J4 drive to a legacy QD75MH/QD77MS positioning module causes the bus to automatically operate in legacy 50 Mbps SSCNET III compatibility mode.