HIGH SPEED STRIP THICKNESS CONTROL Principles and components Requirements for a high speed strip thickness control are a quick and well-designed servohydraulic mill screwdown and highly accurate strip thickness gauges with sufficiently fast response times. The variations of the control scheme are many: Position control, direct roll gap control, roll force control, mass flow control, feedback control, feedforward control and more that combine these modes. Depending on the type of mill, the strip material and other factors, we will create a control scheme for the specific mill that will achieve the required close strip thickness tolerances. Adaptation of processor concept to the requirements The performance data of the different mills vary widely from each other. To achieve equally good finished strip tolerances, the requirements for the control are significantly higher for strip speeds of 1000 m/min, for example, than for strip speeds of 100 m/min. Vollmer control systems are also adapted to the requirements of the mill with regard to the processor hardware (from the high-speed VME-Bus processor to the less expensive PLC assembly), so that the customers´ requirements will be satisfied by an optimal solution. Speed measurement In addition to the strip thickness, the strip speed is an important factor in many control schemes. We apply non-contact laser speedmeters where necessary. On many mills, the use of rotary sensors on the deflector rolls is sufficient. Which type of speedmeter applied, depends on the strip acceleration, the wrap angle on the deflector rolls and other factors.