Slipping Motor Tach Coupling
A reliable speed control in the different sections of a tissue machine is mandatory to ensure optimal machine performance and product quality. Each of these speed control loops rely on motor speed feedback measurement from a tach or encoder.
A defective speed measurement due to electrical or mechanical issue such as broken or slipping tach coupling will lead to speed instabilities. This will not show obvious signs in the absence of a continuous high speed data analysis based on machine specific algorithms.
Detection
This was the case on one of our clients’ tissue machine which they operate in two different modes: Atmos or Conventional. While they were operating in Atmos mode, the belt guide mechanism which is disengaged in this mode began exhibiting abnormal speed variations.
One of the 255 kpis we generate hourly to monitor this machine alerted our specialists of this issue. The belt roll speed reference was stable, but the abnormal variations in the speed regulator output and motor torque revealed that this was another case of a defective speed feedback.
Our Intervention
A shutdown was planned with specific spare parts at hand in prevision of the potential repairs.
Upon inspection, the mill discovered that the belt guide motor tach coupling was slipping.
A simple tightening of the coupling re-stabilized the speed control of the belt guide.
We confirmed that the speed stability was restored and they switched to the conventional mode to fill in the orders that had been on standby.
Benefits
Early detection of this issue represented considerable savings to the mill by secured the product quality and made the E&I team ready to tackle the issue effectively leading to minimized downtime.