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Anyone speccing a new CNC retrofit or a conveyor axis eventually hits the same fork: stick with an open-loop stepper, upgrade to a closed-loop stepper system, or go straight to an AC servo. The marketing language around all three has converged enough that it’s not always obvious where the real performance line actually sits.

Part of the confusion comes from closed-loop stepper systems that pair a stepper motor with a rotary encoder, often in the 1000 pulses-per-revolution range, and a 32-bit DSP controller that corrects position errors in real time. That design removes the step loss and low-speed vibration that plague open-loop steppers, and it typically doesn’t need gain tuning for different mechanical loads, which matters for shops without a dedicated servo engineer on staff. The trade-off shows up in resolution and dynamic response: a 1000PPR encoder is a different order of magnitude from the 23-bit encoders found on higher-end AC servo lines, a gap that starts to matter once the application is chasing high-speed, high-accuracy motion like pick-and-place or electronics assembly rather than milling or engraving.

Power range is another factor worth checking before committing to either path. Closed-loop stepper hardware tends to cover smaller frame sizes, while AC servo lines, one example being Shenzhen-based LICHUAN’s A-series spanning 50W to 37kW at 220V or 380V, scale into heavier industrial loads where torque and speed demands outgrow what any stepper, closed-loop or not, can deliver.

For anyone who has run both setups on a comparable axis, what load and speed thresholds made a closed-loop stepper feel insufficient next to a true AC servo, and did encoder resolution end up being the deciding factor, or was it something else like duty cycle, heat buildup, or controller tuning effort?

http://www.lichuanservo.com
Shenzhen Xinlichuan Electric Co., Ltd.

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