Virtual Shaft

“VIRTUAL SHAFT” APPLICATION

Abstract : The “virtual shaft” is a software developed by ARABB that replaces an emulates a solid mechanical coupling between two motors. It was specially created forreplacing the mechanical clutch that couples the screws of one Tandem Cold Mill stands. It´s working at Siderar (Ensendada plant) since November 2000.
Miguel J. Trulos

1. INTRODUCTION
Themechanical (or hydraulic) screws in a rolling mill stand are used to press the strip, producing then a roll force, and affecting the strip thickness. Considering the mechanical screw down types, the levellingoperation moves the screws in different directions. When one screw moves up, the opposite one moves down. This operation is normally used to reach the level needed by the process. After the desiredlevel is obtained, the screws are usually controlled by the Automatic Gauge Control (AGC). During the rolling process the AGC moves the screws in the called “coupled run” mode. This mode is also usedfor positioning the main mill rolls. In “coupled run” mode both screws have to move in the same direction, maintaining the relative position between them. This is usually done with a mechanical clutch.We developed a special software that can replace the clutch, emulating a solid shaft. We called it “virtual shaft”. The clutch needs high maintenance and in some cases it is too difficult to accessit. The mechanical clutch can be replaced with the “virtual shaft”, introducing high advantages in the mill operation.
clutch M1 M2

Fig. 1 - Rolling mill stand

The main advantages of the“virtual shaft” are: - Maintenance free, no wear. - Better time response (no clutch coupling time) - Redundant system. Option to work with “virtual shaft” or with clutch. - No operation costs. This softwarecan also be used in general applications where it is important to synchronise the position between two or more motors, i.e. EOT crane bridge travel. An encoder coupled directly to motor shaft...