The FX3U-2PG is Mitsubishi Electric’s 2-axis pulse output positioning special adapter for the MELSEC FX3U compact PLC series, providing two independent dedicated high-speed pulse output channels at up to 100 kHz each for stepper motor or servo drive positioning — adding two simultaneous positioning axes to any FX3U base unit via the left-side special adapter interface without consuming any extension bus slot. As the 2-axis variant in the FX3U pulse positioning adapter range, the FX3U-2PG provides twice the axis count of the FX3U-1PG in the same single adapter housing, enabling complete 2-axis independent positioning control (XY table, dual-axis indexer, parallel conveyor drives) from a single adapter module connected to any FX3U base unit. The FX3U-2PG is available through Atlantech Drives — quote within 24-48 hours, worldwide express shipping, 12-month warranty.
What Is the FX3U-2PG?
The FX3U-2PG is a MELSEC FX3U series special function adapter module providing two independent channels of open-collector pulse positioning output, each operating at up to 100 kHz. Both axes are physically housed in the same adapter module and share the left-side special adapter bus connection to the FX3U base unit — the adapter presents two logical positioning controllers to the FX3U CPU, each accessed via its own buffer memory address range using FROM/TO instructions or GX Works2 auto-refresh. Each axis independently stores up to 600 positioning patterns in the adapter’s non-volatile flash memory, provides dedicated external input terminals for near-point DOG and limit switches, and supports manual pulse generator (handwheel) input for manual jog operation. The two axes of the FX3U-2PG operate independently — axis 1 can be executing a homing sequence while axis 2 executes a positioning move simultaneously — but do not support coordinated interpolated motion between the two axes. For applications requiring true linear interpolation between two axes (diagonal straight-line motion), the FX3U-20SSC-H special adapter or a MELSEC-Q QD75D2 positioning module must be specified instead.
Key Technical Specifications
- Model: FX3U-2PG
- Controlled Axes: 2 (independent)
- Connection Interface: FX3U left-side special adapter bus
- Output Type: Open-collector transistor, step/direction or CW/CCW (per axis)
- Maximum Output Pulse Frequency: 100 kHz per axis
- Positioning Patterns per Axis: 600
- Position Data Range: -2,147,483,648 to +2,147,483,647 pulses
- Speed Range: 1 to 100,000 pps per axis
- Acceleration/Deceleration: Trapezoidal (configurable per axis)
- Manual Pulse Generator Input: Supported per axis (×1, ×10, ×100)
- External Signals per Axis: Near-point DOG, upper/lower limit switches
- Current Consumption (adapter bus): 0.15 A at 5 VDC
- Operating Temperature: 0°C to 55°C
- Weight: Approx. 0.18 kg
Typical Industrial Applications
The FX3U-2PG is deployed in 2-axis independent positioning applications where the FX3U base unit’s built-in Y0/Y1 pulse outputs are already allocated to other functions or where a dedicated adapter-based solution provides cleaner axis management than mixing built-in and adapter-based pulse outputs. In dual-axis labelling machines, the FX3U-2PG independently controls the X-axis label transport stepper drive and the Y-axis dispensing head positioning servo — both axes home at power-up and execute independent position sequences triggered by the CPU program based on product sensor inputs, without axis coordination requirements. Dual-axis screw dispensing systems for printed circuit board assembly use the FX3U-2PG for independent XY table control, where the screw head repositions between fastening points at speed while the FX3U CPU manages the torque monitoring and fastening sequence logic. In two-spindle vertical machining centres for educational and prototyping environments, the FX3U-2PG controls X-axis and Z-axis stepper drives independently — the simple positioning functionality of the adapter (preset position, home return, JOG) is sufficient for basic milling operations where linear interpolation is not required. Automated component insertion machines for through-hole PCB assembly use the FX3U-2PG to coordinate the insertion head Y-axis (approach/retract) and the board transport X-axis (step advance) independently, with the CPU sequencing the two axes in alternating operational phases rather than simultaneous interpolated motion.
Maintenance Tips
The FX3U-2PG’s left-side adapter bus connector is a direct board-to-board connection between the adapter PCB and the FX3U base unit’s left adapter interface — there is no cable between the adapter and base unit, and the mechanical connection is maintained by the adapter housing’s snap-fit engagement. In high-vibration environments, inspect the FX3U-2PG’s engagement with the base unit annually — a partially disengaged adapter can cause intermittent communication errors between the adapter and CPU that manifest as unpredictable axis behaviour. Re-engage the adapter by pressing firmly against the base unit until the locking tab clicks fully into position. The FX3U-2PG’s non-volatile positioning pattern memory does not require periodic backup under normal operation, but always maintain a GX Works2 project file backup containing the current positioning pattern data — if the adapter is replaced, the positioning data must be reloaded via GX Works2’s special adapter parameter write function as the replacement adapter ships with factory default (empty) positioning data. For stepper motors connected to the FX3U-2PG outputs, verify the flyback diode installation on each stepper driver’s 24 VDC coil supply annually — stepper drivers with inadequate internal snubbing can generate voltage spikes on the FX3U-2PG open-collector output lines during phase switching, and repeated overvoltage exposure degrades the output transistors over time even if no immediate failure occurs.
Frequently Asked Questions
Q: When using the FX3U-2PG alongside the FX3U base unit’s built-in Y0 and Y1 pulse outputs, how many total independent positioning axes are available?
A: A single FX3U base unit with one FX3U-2PG adapter provides four independent positioning axes: Y0 and Y1 on the base unit (via DRVI/DRVA instructions), plus the two axes of the FX3U-2PG (via FROM/TO buffer memory instructions). If a FX3U-1PG adapter is also installed alongside the FX3U-2PG (consuming two of the four available adapter slots), a fifth independent axis is available — giving a maximum of five independent pulse positioning axes from a single FX3U system with two adapter modules.
Q: Can the FX3U-2PG’s two axes execute home return operations simultaneously?
A: Yes. Both axes of the FX3U-2PG execute their positioning and home return operations autonomously and simultaneously — axis 1 home return and axis 2 home return can be initiated in the same CPU scan cycle by setting the respective home return start bits in each axis’s buffer memory simultaneously. The adapters execute the home return independently for each axis, with each axis’s home sensor (DOG input) and limit switches monitored separately. Both axes must complete their home return operations before the CPU program typically clears the home return complete flag and proceeds with normal positioning operation.
Q: What is the physical difference in size and weight between the FX3U-1PG and FX3U-2PG adapters?
A: The FX3U-2PG is slightly larger and heavier than the FX3U-1PG to accommodate the additional axis output circuit and external signal input terminals — the FX3U-2PG weighs approximately 0.18 kg versus 0.12 kg for the FX3U-1PG, and is approximately 15 mm wider. Both adapters use the same left-side adapter bus interface and can be installed in any of the four adapter positions on the FX3U base unit, with GX Works2 automatically assigning the correct buffer memory addresses based on the configured adapter position and type.
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