The QD75D4 is Mitsubishi Electric’s 4-axis open-collector pulse train positioning module for the MELSEC-Q programmable controller series — providing open-collector pulse output at up to 200 kpps per axis for positioning control of up to 4 independent servo or step motor axes via MR-J4-A, MR-J3-A, MR-J2S-A, or compatible servo amplifiers and step motor drivers with open-collector pulse train input, delivering multi-axis coordinated motion control from a MELSEC-Q base unit in cost-sensitive applications where the lower pulse frequency of open-collector output is adequate and the higher-speed differential output of the QD75MH4 is not required. Atlantech Drives holds stock of the QD75D4. Contact us for fast worldwide delivery and competitive pricing.
What Is the QD75D4?
The QD75D4 is a MELSEC-Q series intelligent positioning module providing 4 independent servo axis channels with open-collector pulse output at up to 200 kpps per axis and open-collector encoder input for closed-loop position verification. The «D» in the model designation indicates the open-collector pulse output type — as distinct from the «MH» differential line driver (RS-422A) output of the QD75MH4, which provides 4 Mpps maximum frequency. The «4» indicates 4-axis capacity, matching the QD75MH4 in axis count while differing in output type. The QD75D4’s 200 kpps maximum pulse frequency is adequate for most step motor driver applications (step motor drivers typically limit to 50–200 kpps for practical operating speeds) and for servo amplifiers in applications where the axis speed and encoder resolution combination does not require more than 200 kpps at maximum traverse speed. Each of the QD75D4’s 4 axis channels independently manages position command pulse generation, encoder pulse counting, home return operation, speed control, and positioning data management — the same complete positioning function set as the QD75MH4, with the positioning data table (up to 600 position points per axis) stored in non-volatile module memory and executed from a single CPU start command. The QD75D4 supports 2-axis linear interpolation between any axis pair, consistent with the QD75MH4 capability.
Key Technical Specifications
- Model: QD75D4
- Axes: 4 independent positioning axes
- Pulse Output Type: Open-collector (NPN), up to 200 kpps per axis
- Encoder Input: Open-collector (NPN), up to 200 kpps per axis
- Position Data: Up to 600 positioning points per axis (non-volatile module memory)
- Interpolation: 2-axis linear interpolation (any axis pair)
- Home Return Methods: Near-point dog, count, data set, stopper, and others
- Control Modes: Position control, speed control, speed-position switching, position-speed switching
- Compatible CPUs: MELSEC-Q Q02UCPU and compatible Q-series CPUs
- Installation: Q-series base unit intelligent function module slot
- Power Consumption: 5 VDC internal bus, approx. 0.75 A
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 27.4 mm × 98 mm × 90 mm
- Weight: Approx. 0.15 kg
Series Comparison & Selection Guide
The QD75 positioning module range for MELSEC-Q includes two physical output types at two axis counts: the QD75D series (open-collector, D suffix) and the QD75MH series (differential RS-422A, MH suffix), each available in 1-axis (QD75D1/QD75MH1), 2-axis (QD75D2/QD75MH2), and 4-axis (QD75D4/QD75MH4) configurations. The QD75D4 (open-collector, 4 axes, 200 kpps) is selected when the application’s axis speed and encoder resolution combination does not require more than 200 kpps, when the servo amplifier or step motor driver accepts only open-collector pulse input (not differential), or when cost reduction versus the QD75MH4 is a project priority. The QD75MH4 (differential RS-422A, 4 axes, 4 Mpps) is selected when higher axis speed requires more than 200 kpps pulse frequency, when superior noise immunity of RS-422A differential output is required in noisy panel environments, or when connecting to servo amplifiers specified for differential pulse input (MR-J4-A recommends differential for maximum performance). In practical terms: a 1 kW MR-J4-100A servo motor with 22-bit encoder at 3,000 rpm maximum speed generates a maximum pulse frequency of (3,000 rpm / 60) × 262,144 pulses/rev = 13.1 Mpps — far exceeding the QD75D4’s 200 kpps limit at the motor’s full speed. However, if the maximum commanded axis speed is limited to (200 kpps × 60) / 262,144 = approximately 46 rpm, the QD75D4 is adequate. For step motor drives typically running at 1,000–2,000 steps/second (1–2 kpps), the QD75D4’s 200 kpps is more than adequate for all practical step motor speeds.
Installation Advice
The QD75D4’s open-collector pulse outputs use NPN transistors pulling the output terminal to 0 VDC when active — the servo amplifier or step motor driver’s pulse input must accept NPN open-collector signals at the QD75D4’s output voltage level. Verify the servo amplifier’s pulse input current requirement against the QD75D4’s output current capacity (typically 10–20 mA per output) — if the servo amplifier’s pulse input draws more current than the QD75D4 output can source, a buffer transistor circuit between the QD75D4 output and the servo amplifier pulse input is required. For open-collector pulse wiring from the QD75D4 to the servo amplifier, use shielded cable for the pulse and direction signals and keep the cable length below 2 metres where possible — open-collector signals at 200 kpps with cable lengths above 2 metres in electrically noisy panels can develop noise-induced false pulses that cause axis position errors. For longer cable runs (above 2 metres), specify the QD75MH4 with differential RS-422A output instead of the QD75D4, as RS-422A differential signals have inherent common-mode noise rejection that enables reliable operation over longer cable runs in noisy environments. Configure the QD75D4’s pulse output type parameter to match the servo amplifier’s expected pulse format — the QD75D4 supports forward/reverse pulse (CW/CCW) format and pulse/direction format; verify the servo amplifier parameter for pulse input format selection and ensure both module and amplifier are configured for the same format before servo axis commissioning.
Frequently Asked Questions
Q: Can the QD75D4 control both servo amplifiers and step motor drivers simultaneously on different axis channels?
A: Yes. Each of the QD75D4’s 4 axis channels independently generates open-collector pulse output — one channel can connect to an MR-J4-A servo amplifier, another to a step motor driver, and the remaining channels to other servo or step motor drives. The QD75D4 manages all 4 axes independently with their respective motion profiles, homing sequences, and positioning data tables — the axis type (servo or step motor) only affects the connected device, not the QD75D4’s internal operation.
Q: What happens to the QD75D4 positioning axes if the MELSEC-Q CPU enters STOP mode during a positioning move?
A: When the MELSEC-Q CPU enters STOP mode during a QD75D4 positioning move in progress, the QD75D4’s internal positioning processor completes the current positioning operation to the target position before stopping — or immediately stops pulse output depending on the QD75D4’s «stop at CPU STOP» parameter setting. Configure the parameter based on the application’s safety requirement: «stop immediately» is appropriate for most machine safety scenarios where axis motion should stop when the PLC program stops; «complete to target» may be appropriate for press feed or packaging applications where stopping mid-stroke causes product damage.
Q: Can the QD75D4 accept encoder feedback from the servo motor encoder for closed-loop position verification?
A: Yes. The QD75D4 includes open-collector encoder input on each axis channel for connecting to the servo amplifier’s encoder output (typically an A-phase, B-phase, Z-phase open-collector output available on MR-J4-A servo amplifiers). The QD75D4 counts the encoder feedback pulses independently of the command pulse output and compares the two for position error detection — the module can generate a position error alarm if the encoder count deviates from the command count by more than the configured allowable error, providing closed-loop position verification at the module level without PLC ladder programming.
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