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

Position deviation too large error - root causes?

tom_diedesign

Getting "position deviation too large" errors on our 300T servo press, but only on one specific die. All other dies run fine. The error happens about 1 in 20 strokes, always during the forming portion of the stroke.

Die is a heavy coining operation, probably using 80% of press capacity. The parts look fine even when the alarm triggers — dimensions are all in spec.

Is this a tuning issue? Should I widen the position deviation window for this die? Or is the press telling me something is actually wrong?

anna_plc

Increasing the deviation limit is the wrong fix —it just masks the problem. The real question is: why is the motor falling behind the commanded position? Three common causes: 1) Forming force exceeds motor torque capacity at that slide position. 2) Mechanical binding (gibs too tight). 3) Gain settings too low for the load. Check motor current during the fault —if it's at the limit, the motor can't keep up.

jim_apps

On heavy forming jobs, the position deviation often spikes at the moment of material contact because the load changes suddenly. The solution isn't to increase the limit —it's to reduce the approach speed so the load transition is more gradual. Slow down the last 10-15mm before contact and the deviation spike drops dramatically.

raj_pm

One thing nobody mentioned yet — check your encoder cable routing. I had a press throwing random position deviation faults and it turned out the encoder feedback cable was running parallel to the main power cables for about 2 meters. EMI was corrupting the position feedback intermittently.

Moved the encoder cable to the other side of the cabinet, added a ferrite choke at the drive end, faults dropped to zero. Took 20 minutes to fix what we spent 3 weeks chasing through gain tuning and mechanical checks.

Also worth checking: if you have an absolute encoder, verify the multi-turn counter hasn't drifted. Power cycle the drive and compare the displayed position to a dial indicator on the slide. I've seen 0.02-0.03mm drift accumulate over months on Heidenhain encoders that were technically "in spec" but enough to trigger deviation alarms during high-force forming.

toolndye_dave

Coming back to this one — we had another position deviation mystery last month that's worth sharing. Press was throwing the fault only on one specific die, and only after about 200 cycles. Turned out the ball screw was developing a thermal preload issue.

Here's what was happening: the ball screw heats up during continuous running (ours was hitting 45°C after 20 minutes), the thermal expansion increases the preload, and eventually the motor can't push through the added friction at the bottom of the stroke. The deviation would spike to 0.04mm right at BDC — just enough to trip the alarm.

Diagnosis was simple once we knew what to look for: put a non-contact IR thermometer on the ball screw nut housing. If it's climbing past 40°C and the faults correlate with temperature, that's your answer. Fix was adjusting the preload spec from the factory-default 0.03mm to 0.05mm to allow for thermal growth. Haven't seen the fault since.

The other thing I'd add to what anna_plc said about gains — if you're on Yaskawa, check Un025 (torque command monitor) during the fault. If it's hitting 100% at the moment of deviation, the motor is genuinely torque-limited and no amount of gain tuning will help. You either need to slow down the forming segment or you're undersized for the job.