What is a servo press?

A servo press uses servo motors for precise force and position control during forming operations.

How do I calculate servo press tonnage?

Use our free tonnage calculator at servopress.club/tonnage-calculator.html

Yaskawa Sigma-7 A.C90 Alarm: Encoder Communications Error on Servo Press

admin

The A.C90 alarm (Encoder Communications Error) on Yaskawa Sigma-7 drives is particularly common on servo press applications due to the vibration environment.

Root Causes (in order of frequency):
1. Encoder cable damage: The cable flexes with every stroke. Check for cuts, pinching, or tight bend radii. Minimum bend radius: 10x cable diameter.
2. Connector contamination: Oil mist and metal particles get into the encoder connector. Clean with contact cleaner and apply dielectric grease.
3. Ground loop: If the encoder cable shield is grounded at both ends, a ground loop can cause intermittent errors. Ground at drive end only.
4. Vibration-induced connector loosening: Add a cable strain relief within 150mm of the motor on high-SPM presses.
5. Encoder failure: Run the encoder diagnostic in SigmaWin+ software.

Temporary Workaround: Reduce SPM by 30% and monitor. The alarm is often intermittent at lower speeds, giving you time to order the cable or encoder.

anna_controls

A.C90 on Yaskawa is almost always a physical connection issue in my experience. The encoder connector on Sigma-7 has a locking tab that wears out over time from vibration. I add a zip tie as secondary retention on every installation. If you are getting intermittent A.C90, try pressing the connector firmly while the drive is powered. If the alarm clears, the connector is the problem.

dave_toolmaker

A.C90 in a vibration environment: check the encoder connector locking mechanism. The standard Yaskawa encoder connector has a latch that can vibrate loose over time. We add a cable tie as a secondary retention on every encoder connector. Cheap insurance against intermittent A.C90 faults that are impossible to reproduce on the bench.