The QD75D2 is Mitsubishi Electric’s 2-axis positioning module for the MELSEC-Q programmable controller series, providing differential line driver pulse output for precise open-loop position control of stepper motors and servo drives equipped with pulse train input interfaces — enabling coordinated 2-axis positioning, linear interpolation, and speed control directly from the MELSEC-Q controller without a dedicated motion CPU. As the 2-axis differential output variant of the QD75 positioning module family, the QD75D2 delivers high-speed pulse output at up to 4 Mpps per axis with superior noise immunity compared to open-collector pulse output modules, making it the preferred specification for high-speed stepping systems and long-cable servo drive connections where differential signalling is essential for reliable pulse transmission. Atlantech Drives holds stock of the QD75D2. Contact us for fast worldwide delivery and competitive pricing.
What Is the QD75D2?
The QD75D2 is a MELSEC-Q series intelligent positioning module providing two independent axes of pulse train position control. Each axis generates step and direction (or CW/CCW pulse) output signals using RS-422A differential line driver circuitry, providing balanced differential signals that reject common-mode noise on cable runs up to 10 m between the QD75D2 and the servo drive or stepper driver. The module stores positioning data (target positions, speeds, acceleration/deceleration times, and positioning patterns) in its own non-volatile internal memory, executing position profiles autonomously without consuming CPU scan time once a positioning operation is started by the CPU program. Up to 600 positioning patterns per axis can be stored in the QD75D2’s internal data memory, enabling complex multi-step position profiles (approach, index, dwell, return sequences) to be executed without repeated CPU involvement. The QD75D2 interfaces with the MELSEC-Q CPU via the high-speed internal bus using FROM/TO instructions or GX Works2 auto-refresh, with the CPU writing positioning commands to the module’s buffer memory and reading position feedback (current position, operation status, error codes) from the buffer memory in return.
Key Technical Specifications
- Model: QD75D2
- Controlled Axes: 2 (independent)
- Output Type: Differential line driver (RS-422A), step/direction or CW/CCW
- Maximum Output Pulse Frequency: 4 Mpps per axis
- Positioning Patterns per Axis: 600
- Interpolation: Linear interpolation between 2 axes
- Position Data Range: -2,147,483,648 to +2,147,483,647 pulses
- Speed Range: 1 to 4,000,000 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): 0.55 A
- External Power Supply: 24 VDC ±10%, 0.10 A (required for output circuit)
- Operating Temperature: 0°C to 55°C
- Weight: Approx. 0.25 kg
Typical Industrial Applications
The QD75D2 is commonly deployed in 2-axis positioning systems requiring coordinated motion without the cost and complexity of a dedicated motion controller. In gantry loading systems for machine tool tending, the QD75D2 controls the X and Y axes of a Cartesian robot using stepper motors — the module’s built-in linear interpolation function generates smooth diagonal moves between positions without jerky axis-sequential motion. Automated screw dispensing and adhesive dispensing systems in electronics assembly use the QD75D2 for XY table control, where the 4 Mpps output frequency enables high-speed positioning between dispensing points to maximise throughput. Label printing and applying machines in packaging lines use the QD75D2 to synchronise the label unwinding servo axis with the conveyor speed pulse input — the module’s speed synchronisation function tracks the external pulse input and maintains a configurable gear ratio between the conveyor and the label applicator. In CNC-like engraving and marking systems for industrial identification, the QD75D2 provides the 2-axis coordinated motion for simple profile generation using the module’s built-in linear and arc interpolation, reducing the programming complexity compared to implementing custom interpolation in the MELSEC-Q CPU ladder program.
Maintenance Tips
The QD75D2’s internal non-volatile memory retains all positioning data (patterns, parameters, and home position data) across power cycles without battery backup. However, if the module is replaced, all positioning data must be reloaded from a GX Works2 project file — always maintain an up-to-date GX Works2 backup of the QD75D2 positioning data as part of the machine documentation, enabling rapid module replacement without manual re-entry of positioning parameters. For systems using external incremental encoders connected to the QD75D2’s feedback input, verify encoder cable shielding and grounding annually — encoder cable shield currents induced by adjacent VFD cables are a common cause of false position feedback pulses that accumulate as position drift over time. If unexplained position offset develops in a system that was previously accurate, check the encoder signal quality by monitoring the QD75D2’s error detection register for pulse error counts via GX Works2’s buffer memory monitor — even a small number of miscounted encoder pulses per machine cycle will accumulate into measurable position error over hundreds of cycles. For stepper motor systems using the QD75D2 without position feedback, verify the motor’s step loss immunity by checking the maximum load inertia ratio at the commanded acceleration rate — a QD75D2 accelerating a stepper system beyond the motor’s pull-in torque curve will cause step losses that are undetected by the positioning module, resulting in position errors that persist until the next home reference cycle.
Frequently Asked Questions
Q: Can the QD75D2 perform linear interpolation between its two axes simultaneously?
A: Yes. The QD75D2 includes built-in 2-axis linear interpolation, generating coordinated pulse outputs on both axes simultaneously to move the controlled mechanism along a straight-line path between two positions at the configured speed. The interpolation algorithm calculates the required pulse ratio between the two axes to maintain a straight-line trajectory, eliminating the need for CPU-based interpolation calculations. Arc interpolation is supported by the 4-axis QD75MH4 but is not available in the 2-axis QD75D2.
Q: What is the difference between the QD75D2 differential output and the QD75P2 open-collector output?
A: The QD75D2 uses RS-422A differential line driver output (balanced, ±5V swing), while the QD75P2 uses open-collector output (single-ended, 0–24V). Differential output provides superior noise immunity for cable runs longer than 2–3 m and is required for servo drives with RS-422A pulse input specifications — most mid-to-high performance servo drives (Mitsubishi MR-J4, Yaskawa Σ-7, Panasonic MINAS A6) use differential pulse input. Open-collector output is appropriate only for short cable runs to stepper drivers or low-cost servo drives that do not support differential input.
Q: Can the QD75D2 accept manual pulse generator (MPG/handwheel) input for manual axis jogging?
A: Yes. The QD75D2 supports manual pulse generator input on each axis via dedicated MPG input terminals, allowing operators to manually jog axes using a handwheel encoder for precise manual positioning. The MPG multiplication factor (×1, ×10, ×100 pulse magnification) is configurable via buffer memory parameters in GX Works2, enabling coarse and fine manual positioning from the same handwheel.
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