A pick-and-place machine that occasionally misses steps at 200 picks per minute is usually not a hardware failure—it's a pulse interface mismatch between the PLC and the servo drive. The Coolmay PLC sends position commands as pulse trains, and the EMSD5 servo drive interprets them. When the electrical characteristics of those pulses don't match what the drive expects, the motor loses position and the machine produces scrap.
The EMSD5 accepts three types of pulse inputs, and matching the PLC output to the correct input mode is the most critical wiring decision:
| PLC Output Type | EMSD5 Setting (Pn300) | Signal Wiring |
|---|---|---|
| NPN open-collector (24 V) | Pn300 = 0 (Pulse + Direction) | Pulse → PULS+ / PULS-; Direction → SIGN+ / SIGN- |
| PNP sourcing | Requires level shifter or use differential | Use an external translator or switch PLC output type |
| Differential line driver (5 V) | Pn300 = 2 (Differential) | A+ → PULS+, A- → PULS-, B+ → SIGN+, B- → SIGN- |
The input mode selection matters because the EMSD5's maximum pulse frequency depends on it. In differential mode, the drive accepts up to 500 kHz, which supports high-speed operation. In open-collector mode, the limit drops to 200 kHz, and a 2.2 kΩ pull-up resistor to 24 V is required at the drive input.
Electronic gear ratio configuration is where most pulse-counting errors originate. The EMSD5 encoder resolution is 131,072 pulses per revolution (17-bit). On a ballscrew with a 10 mm lead, setting Pn308 (numerator) to 131,072 and Pn309 (denominator) to 10,000 gives you 1 µm of linear travel per command pulse. Getting this wrong by a factor of ten is easy to do and produces positioning errors that look like mechanical problems.
A few field-proven wiring practices eliminate the most common pulse-related issues. Use shielded twisted-pair cable (AWG 24, 120 Ω characteristic impedance) for the pulse lines and keep the cable under 10 meters. Separate pulse wiring from motor power cables by at least 100 mm. If the motor jitters at low speed, increase the electronic gear ratio. If it misses steps at high speed on open-collector output, switch to differential mode by setting Pn300 to 2.
For high-speed pick-and-place systems, the Coolmay series PLC with differential pulse output driving the EMSD5 servo in differential mode (Pn300 = 2) delivers reliable positioning at speeds up to 2500 RPM with zero pulse loss.
Download the EMSD5 wiring guide including electronic gear ratio calculators for common ballscrew pitches. Contact our application engineers for assistance configuring multi-axis pulse synchronization.
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