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 Tonnage Monitoring Without a Dedicated System

admin

**Question:** We have a 300-ton servo press but no tonnage monitoring system. We want to detect broken punches and overloads without buying a $15,000 tonnage monitor. Can we use the servo drive data?

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**Answer:**

Yes, you can use servo drive torque data as a proxy for tonnage monitoring. It is not as accurate as a strain gauge system, but it can detect broken punches and significant overloads.

## Using Drive Torque as Tonnage Proxy

The servo drive reports motor torque in real time. Torque is proportional to forming force (with some losses from the mechanical transmission).

**How to access torque data:**
- Siemens SINAMICS: r0080 (torque actual value, in Nm)
- Yaskawa: Un000 (torque reference monitor)
- Mitsubishi MR-J4: monitor parameter Md.Trq (torque)
- ABB ACS880: parameter 01.10 (motor torque %)

## Setting Up Monitoring

1. **Establish baseline**: run 50 good parts and log the peak torque value for each stroke. Calculate the average and standard deviation.

2. **Set limits**:
- High limit (overload): average + 3 standard deviations (typically 110-120% of average)
- Low limit (broken punch): average - 3 standard deviations (typically 70-80% of average)

3. **Configure drive fault output**: most drives can output a digital signal when torque exceeds a threshold. Wire this to the press safety circuit to stop on overload.

## Limitations vs. Dedicated Tonnage System

- Cannot distinguish between different punches in a progressive die
- Torque-to-force conversion changes with wear and lubrication
- Response time is 1-5ms vs. 0.1ms for strain gauges
- Cannot detect gradual punch wear (only sudden changes)

## Low-Cost Hardware Option

A load cell under one of the press columns connected to a simple PLC: 50-ton load cell costs $200-$500, basic PLC with analog input costs $300-$800. Total under $2,000 for a functional tonnage monitor.

anna_controls

Yes, you can use the servo drive's current data as a proxy for tonnage. Motor current is proportional to torque, and torque is proportional to force (through the mechanical linkage). On Yaskawa, monitor Un000 (torque reference). On Siemens, monitor r0079. It's not as accurate as strain gauge monitoring but it catches broken punches and gross overloads.

lisa_quality

We did exactly this on our 300T press. Set up the drive to output an analog signal proportional to torque, fed it into our data acquisition system, and built force envelopes for each die. Catches about 85% of what a dedicated tonnage monitor would catch. Not perfect but way better than nothing for $500 in parts.