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

Servo Press Position Deviation Too Large Error: Root Causes and Fix

admin

**Question:** Our servo press throws "position deviation too large" during the forming stroke on heavy jobs. It does not happen on light jobs. We increased the deviation limit in the parameters but it came back. What is actually causing this?

---

**Answer:**

"Position deviation too large" means the actual slide position is falling behind the commanded position by more than the allowed tolerance. Increasing the limit is a workaround, not a fix.

## Why It Happens on Heavy Jobs

During the forming stroke, the press encounters high resistance from the material. The motor must produce high torque to maintain the commanded velocity. If the motor cannot produce enough torque fast enough, the slide slows down and falls behind the position command.

Root causes:
1. **Motor torque limit reached**: the drive is hitting its current limit and cannot accelerate fast enough
2. **Motion profile too aggressive**: the commanded forming speed is too high for the load
3. **Drive tuning too stiff**: the position loop gain is too high, causing the drive to demand acceleration it cannot deliver
4. **Mechanical binding**: increased friction from worn gibs or insufficient lubrication

## Diagnosis

Check the drive torque during the fault:
- Yaskawa: Un000 (torque reference) - if at 100% when the fault occurs, the motor is at its torque limit
- If torque is below 80%, the problem is tuning or mechanical, not motor capacity

## Fix Based on Root Cause

**If motor is at torque limit:**
- Reduce forming speed in the motion profile (try 80% of current speed)
- Verify the press tonnage rating matches the job requirements

**If tuning issue:**
- Reduce position loop gain (Kp) by 20% and test
- Set deviation limit to a reasonable value (3-5mm during forming) - not unlimited

**If mechanical:**
- Check gib lubrication - dry gibs increase friction significantly
- Measure gib clearance - too tight causes binding
- Check for foreign material in the slide guides

## The Right Deviation Limit

- During approach: 1-2mm deviation allowed
- During forming: 3-5mm deviation allowed (forming loads cause some lag)
- During return: 1-2mm deviation allowed

If you need more than 5mm to avoid false trips, the underlying problem needs to be fixed.

anna_controls

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_applications

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.