Paper Cup Machine Servo Motor Tuning FAQ

How often should paper cup machine servos be re-tuned?

Re-tune after any change that alters the mechanical load path: belt or coupling replacement, gearbox service, tooling or mold change, or a motor swap. In steady production, verify following error once a month and run a full tune again if it drifts past the alarm threshold. A servo that needs weekly re-tuning usually has a mechanical fault — loose coupling, slack belt, or gearbox backlash — not a tuning fault, so fix the mechanics before touching gains.

What inertia ratio should a cup machine servo have?

Keep the load-to-motor inertia ratio below 10:1, and target 3:1 to 5:1 on forming and curling axes that must settle fast. A high ratio forces low gains to stay stable, which shows up as overshoot and slow settling at speed, and it makes the axis behave differently hot and cold. Belt tension, coupling stiffness, and gearbox backlash are the three things that push the ratio up, so measure the ratio after any drivetrain work.

Why does my cup machine servo hum or hunt at standstill?

Standstill hum is almost always a resonance or a gain set too high for the real inertia. Enable the notch filter at the resonant frequency, lower the velocity loop gain until the hum stops, then raise the position gain again. Check belt tension and coupling play first, because a loose belt makes any gain setting unstable. Hum that appears at only one speed is a resonance to notch out; hum at every speed points to excessive gain or a dragging axis.

What order should the servo loops be tuned in?

Tune from the inside out: confirm the current loop and motor constants, stabilize the velocity loop, then add position gain for accuracy, then feedforward to remove lag under acceleration, and finally place the notch filter for resonance. Position gain raised on an unstable velocity loop amplifies noise instead of accuracy, so skipping the order produces a machine that passes auto-tune and then alarms under production load. Auto-tune is a baseline, not an answer — always verify with a step response.

What causes a following-error alarm on a cup forming axis?

Most following-error alarms trace to one of three causes: gains too low for the actual load, mechanical drag from a dry way or stuck bearing, or an inertia ratio that changed when a component was replaced. Re-check the mechanical path, then add feedforward rather than brute-force gain. If the axis follows well at low speed but alarms at high speed, it is a settling problem — tighten the mechanical path and increase feedforward instead of fitting a larger motor.

How do you verify a servo tune before releasing the machine?

Run at target speed and log following error on every axis for a full shift, check cup height, seam overlap, and bottom roundness against the drawing, and listen for hum during idle between jobs. Re-check emergency-stop stopping time because new gains change the deceleration profile, then write the gains, inertia ratio, and filter values into the machine file. A tune is finished only when it survives a real shift with guards closed — three numbers prove it: inertia ratio, following error at speed, and the tuning record.