The QD75P4N is Mitsubishi Electric’s 4-axis open-collector pulse positioning module for the MELSEC-Q programmable controller series, providing independent pulse train position control for four stepper or servo axes simultaneously — the highest axis count available in the open-collector QD75P sub-family — with built-in external encoder feedback input on each axis enabling closed-loop position verification and error detection for applications where the servo drive’s own encoder feedback is not accessible to the positioning module. As the 4-axis enhanced version of the QD75P series, the QD75P4N adds the «N» generation improvements including expanded positioning data memory and enhanced speed synchronisation functions compared to the original QD75P4. Available now at Atlantech Drives with worldwide express delivery and 12-month warranty — complete our quote form for pricing and availability.
What Is the QD75P4N?
The QD75P4N is a MELSEC-Q series intelligent positioning module providing four independent axes of open-collector pulse train position control, each capable of outputting step/direction or CW/CCW pulse signals at up to 200 kpps to stepper motor drivers or servo drives with open-collector pulse train input. The «P» designation indicates open-collector transistor output (as distinct from the «D» differential line driver output of the QD75D2 and QD75MH series), making the QD75P4N appropriate for stepper drivers and servo drives with single-ended open-collector pulse input interfaces — common in entry-level and mid-range servo systems where RS-422A differential input is not available. The «N» suffix denotes a second-generation enhanced model with 600 positioning patterns per axis (versus 255 in the original QD75P4) and improved speed synchronisation accuracy. The external encoder feedback input on each axis accepts AB quadrature signals from a separate encoder mounted on the mechanical load, enabling position verification independent of the motor’s own encoder and detection of mechanical slip or compliance errors that the servo drive’s internal encoder cannot detect.
Key Technical Specifications
- Model: QD75P4N
- Controlled Axes: 4 (independent)
- Output Type: Open-collector transistor, step/direction or CW/CCW
- Maximum Output Pulse Frequency: 200 kpps per axis
- Positioning Patterns per Axis: 600
- External Encoder Input: AB quadrature, per axis (for closed-loop position verification)
- Interpolation: Linear interpolation (2-axis, 3-axis, 4-axis)
- Position Data Range: -2,147,483,648 to +2,147,483,647 pulses
- Speed Range: 1 to 200,000 pps
- Acceleration/Deceleration: Trapezoidal or S-curve (configurable per axis)
- Manual Operation: JOG, inching, manual pulse generator input
- External Signals: Near-point DOG, upper/lower limit switches (per axis)
- Current Consumption (5 VDC internal bus): 0.70 A
- External Power Supply: 24 VDC ±10%, 0.15 A (required)
- Operating Temperature: 0°C to 55°C
- Weight: Approx. 0.30 kg
Series Comparison & Selection Guide
The MELSEC-Q QD75 positioning module family covers axis counts from 1 to 4 in both open-collector (QD75P series) and differential line driver (QD75D and QD75MH series) output variants. The QD75P4N is the correct choice when four axes of open-collector pulse control are required and the servo drives or stepper drivers do not support differential RS-422A pulse input. For applications requiring differential output at 4 Mpps for high-speed servo systems, the QD75MH4 (4-axis SSCNET III/H network servo control) or QD75D series (differential pulse, up to 4 Mpps) should be specified instead. The 200 kpps maximum output frequency of the QD75P4N is the key limitation compared to the 4 Mpps of the QD75D2 — for stepper systems running at speeds up to 3,000 RPM with a 400-step motor (1,600 microstep pulses per revolution at ×4 microstepping), the 200 kpps limit supports a maximum speed of approximately 7,500 RPM equivalent step rate, which is adequate for most slow-to-medium speed stepper applications but insufficient for high-speed servo systems requiring fast positioning. For 4-axis servo applications requiring both high speed and closed-loop control, the QD77MS4 SSCNET III/H module with Mitsubishi MR-J4 servo amplifiers provides full closed-loop servo control without pulse train interface limitations.
Expert Tips
When using the QD75P4N’s external encoder feedback input for load-side position verification, configure the encoder resolution and gear ratio parameters in GX Works2’s positioning parameter editor to match the actual mechanical arrangement — the module uses this information to compare the commanded position (from its internal pulse counter) with the measured position (from the external encoder) and generate a position deviation error if the difference exceeds the configurable allowable deviation. Set the allowable deviation threshold to a value that catches genuine mechanical slip (such as a stepper motor losing steps under overload) while remaining above the normal positional tolerance caused by encoder quantisation, mechanical backlash, and thermal expansion — a threshold of 5–10 encoder counts is appropriate for most applications. For 4-axis systems where all four axes perform simultaneous interpolated moves, verify that the MELSEC-Q CPU’s scan time is fast enough to update all four axes’ speed and position commands within the required motion update interval — if the CPU scan time is longer than the minimum pulse generation period for the commanded speed, the QD75P4N’s internal positioning processor will continue executing the previously commanded profile without waiting for CPU updates, which is the correct behaviour for autonomous positioning execution but requires the CPU to initiate moves correctly before the axis starts rather than updating moves mid-execution. For open-collector output cable runs longer than 3 m, add a 1 kΩ pull-up resistor between the pulse output terminal and the 24 VDC supply at the receiving device end to ensure adequate signal rise time — long cable capacitance slows the open-collector signal rise time, and at 200 kpps the pulse duty cycle leaves only 2.5 µs for each high-to-low and low-to-high transition, requiring adequate pull-up current to maintain clean pulse edges.
Frequently Asked Questions
Q: Can the QD75P4N perform 4-axis simultaneous linear interpolation?
A: Yes. The QD75P4N supports simultaneous linear interpolation across all four axes, generating coordinated pulse outputs on up to four axes to move the controlled mechanism along a 3D or 4D straight-line path at the configured composite speed. The interpolation is executed autonomously by the module’s positioning processor without CPU involvement once the interpolation start command is issued from the ladder program.
Q: What is the maximum cable length for the QD75P4N open-collector pulse output to a stepper driver?
A: Mitsubishi recommends a maximum cable length of 10 m for open-collector pulse output at up to 200 kpps. For longer cable runs, differential line driver output modules (QD75D2 or QD75MH series) should be specified, as differential RS-422A signalling supports cable runs up to 10 m at 4 Mpps with superior noise immunity. If the application genuinely requires open-collector output over distances beyond 10 m, a pulse signal repeater with differential-to-open-collector conversion at the drive end can extend the effective cable length.
Q: Can the QD75P4N’s external encoder input be used as a virtual master axis for electronic gearing?
A: Yes. The QD75P4N supports speed synchronisation mode, in which one axis’s output pulse frequency tracks the input frequency from an external encoder at a configurable gear ratio. This enables electronic gearing between a master axis (encoder) and slave axes (pulse outputs), commonly used in web tension control, packaging film registration, and conveyor synchronisation applications where the slave axis must maintain a fixed speed ratio relative to the master without mechanical gearing.
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