Often in coating applications there is a requirement for a very accurate coater roll positioning system. Many manufacturers provide simple screw actuators and even ‘servo’ actuators but these are not always sufficient.
Centurion Systems designed a servo stepper motor actuator package which has a positioning accuracy of better than 0.0001 inches. The positioning is controlled by a servo PID loop which works to a gap target which is directly measured to better than 0.0001 inch accuracy. This inner control loop has its cascaded set point provided by a scanning sensor measuring either the weight of the coating or the weight of the finished product
As fine a control as this represents the unit must be extremely rugged in order to withstand the normal wear and tear found in manufacturing plants. The coating rolls may bend under the hydraulic forces applied to the rolls, but the actuator system will not move.
Line speed does affect the weight in most coaters therefore line speed variations must be incorporated into the control algorithym of the package. The Centurion Micro Actuator has an imbedded microprocessor which is reading the linear roll displacement 1000 times per second so that if the rolls move due to hydraulic forces the servo control immediately corrects that error. As liner speed varies that too is inputted into the micro controlled and it makes ‘feed forward’ control actions to counter those future errors in coat weight.
The Micro Actuator incorporates these controls within a dedicated computer which does not need to wait for data transfer times or translation times between different time based systems. The corrections are immediate. This is the reason for automatic control, that is to quickly make corrections to errors as soon as they are apparent.