QD77MS4 is a 4-axis Simple Motion Module for Mitsubishi Electric’s MELSEC-Q programmable logic controller platform, providing high-speed synchronized motion control via SSCNET III/H (Serial Synchronous Communication Network III/H) optical fiber interface. Designed as a compact, cost-effective alternative to dedicated motion controllers, the QD77MS4 integrates positioning, synchronous control, and cam functions directly into the Q-series base unit, eliminating the need for a separate motion CPU. The QD77MS4 is available through Atlantech Drives — quote within 24-48 hours, worldwide express shipping, 12-month warranty.
What Is the QD77MS4?
The QD77MS4 belongs to Mitsubishi Electric’s Simple Motion Module family — intelligent function modules that bring servo motion control capability to standard MELSEC-Q PLC systems without requiring a dedicated Q172DCPU or Q173DCPU motion CPU. The «MS4» designation indicates SSCNET III/H interface with 4 controllable axes. Unlike earlier QD75 positioning modules that used pulse train output to connect servo amplifiers, the QD77MS4 communicates with MR-J4 and MR-J5 series servo amplifiers over SSCNET III/H optical fiber at 150 Mbps, providing deterministic 0.888 ms or 1.777 ms servo cycle times and eliminating susceptibility to electrical noise on the motion network. The module supports linear interpolation (up to 4 axes), circular interpolation (2-axis), and helical interpolation, as well as electronic cam profiles for flying shear, rotary knife, and registration mark applications — capabilities previously available only in full motion CPU systems.
Key Technical Specifications
- Number of Controlled Axes: 4 (expandable via SSCNET III/H daisy-chain)
- Communication Interface: SSCNET III/H optical fiber (150 Mbps)
- Servo Cycle Time: 0.888 ms or 1.777 ms (selectable)
- Positioning Data: 600 points per axis
- Interpolation Functions: Linear (up to 4-axis), Circular (2-axis), Helical (3-axis)
- Synchronous Control: Electronic gear, electronic cam (cam data: 65,536 points max)
- Speed Range: 0.01 mm/min to 20,000,000 mm/min (mm-based units)
- Acceleration/Deceleration: Trapezoidal, S-curve, and sine curve profiles
- Compatible Amplifiers: MR-J4-B, MR-J4W-B, MR-J5-B series (SSCNET III/H)
- Current Consumption: 5 V DC, 1.00 A (from Q-bus)
- Operating Temperature: 0 °C to 55 °C
- Dimensions (W × H × D): 27.4 × 98 × 90 mm
- Weight: Approx. 200 g
Series Comparison & Selection Guide
Within the Simple Motion Module family, Mitsubishi offers the QD77MS2 (2-axis), QD77MS4 (4-axis), QD77MS16 (16-axis), and QD77GF4/GF16 variants with SSCNET III/H or CC-Link IE Field Network interfaces. The QD77MS4 is the most commonly selected variant for machine builders requiring between 2 and 4 servo axes with synchronized motion — applications such as dual-axis gantries, 3-axis dispensing systems, and 4-axis assembly robots. For applications requiring more than 4 axes on a single module, the QD77MS16 supports up to 16 axes on a single slot but at a significantly higher module cost; it is typically justified when cabinet space is constrained and the alternative would require multiple QD77MS4 modules. The QD77GF4 replaces the SSCNET III/H interface with CC-Link IE Field for installations where mixed vendor servo drives (non-Mitsubishi) must be controlled from the same PLC — this variant sacrifices the deterministic 0.888 ms cycle time of SSCNET III/H for the more open CC-Link IE Field protocol. For applications requiring fewer than 2 servo axes with simple point-to-point positioning only, the QD75MH2 pulse output module remains a lower-cost option, though it lacks synchronous control and cam functions.
Replacement & Upgrade Notes
The QD77MS4 is the direct functional replacement for the older QD75MH4 4-axis pulse positioning module in systems being upgraded to SSCNET III/H servo amplifiers. The upgrade requires replacing the QD75MH4 with the QD77MS4, replacing any MR-J3 or MR-J2S amplifiers with MR-J4-B (SSCNET III/H) variants, and re-parameterising the positioning data in MT Developer2 or GX Works2. Note that positioning data tables from QD75MH4 projects are not directly importable into QD77MS4 projects — migration must be performed manually or using Mitsubishi’s conversion utility available from the FA Global support portal. When retrofitting an existing MELSEC-Q system, verify that the Q-series CPU firmware supports the QD77MS4; CPUs manufactured before 2012 may require a firmware update. The QD77MS4 is not compatible with older SSCNET (first generation) or SSCNET III (non-H) amplifiers — only SSCNET III/H devices (MR-J4-B and later) are supported on the optical fiber bus.
Frequently Asked Questions
Q: Can the QD77MS4 control stepper motors or only servo amplifiers?
A: The QD77MS4 communicates exclusively via SSCNET III/H optical fiber and therefore requires SSCNET III/H-compatible servo amplifiers (MR-J4-B or MR-J5-B series). It cannot directly drive stepper motors via pulse output. For stepper motor control within a MELSEC-Q system, the QD75MH series pulse output modules remain the appropriate choice.
Q: How many QD77MS4 modules can be installed in a single MELSEC-Q system?
A: Multiple QD77MS4 modules can be installed in the same Q-series base unit, subject to the total I/O slot count and the CPU module’s intelligent function module limit (typically up to 64 modules for Universal model CPUs). Each QD77MS4 controls its own independent 4-axis SSCNET III/H network, so two modules in one rack yield 8 independently controlled axes with separate motion programs per module.
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