Method and control system for applying defined clamping forces

A control system for applying defined clamping forces in a brake that is electrically operable by an actuator and includes a first friction surface (friction lining) and a second friction surface (brake disc), the control system comprising:

• a clamping force sensor (5) for determining a clamping force (F);
• a position sensor (6) for determining the actuator position (φ), wherein a correlation exists between the actuator position (φ) and the clamping force (F);
• a first controller (1), to which signals representative of a clamping force nominal value (Fnominal) and a clamping force actual value (Factual) and signals representative of an actuator position actual value (φmeas) are sent as input quantities, and the output quantity of the first controller corresponds to an actuator speed nominal value (nnominal);
• a second controller (2) that is connected downstream of the first controller and to which signals representative of the actuator speed nominal value (nnominal) and an actuator speed actual value (nactual) are sent as input quantities, and the output quantity of the second controller corresponds to an actuator torque nominal value (Mnominal);
• a third controller (3) that is connected downstream of the second controller and to which signals representative of the actuator torque nominal value (Mnominal) and an actual value (Iactual) of the current to be supplied to the actuator are sent as input quantities, and the output quantity of the third controller represents a correcting variable (U) for adjusting the actual value (Iactual) of the current to be supplied to the actuator;
• and
• an application-point identification module (8), to which signals representative of the actual value of the position (φmeas) measured at the actuator (4) and the actual value of the actuating force (Fmeas) measured at the actuator (4) are sent as input quantities, and the output quantity of which represents a value (φ0) of the actuator position, which corresponds to the application of the first friction surface on the second friction surface, with the signal representative of the actuator position actual value (φactual) being produced by subtraction of the value (φ0) from the signal representative of the value of the measured actuator position (φmeas), wherein the application-point identification module (8) includes low-pass filters (12, 13) of nth order for low-pass filtering of signals representative of the actual value of the position (φmeas) measured at the actuator (4) and the actual value of the actuating force (Fmeas) measured at the actuator (4), and differentiators (14, 15) are connected downstream of the low-pass filters for producing the time derivative of the filtered signals of the actuator position ((φmeas,filt) and the clamping force (φmeas,filt), the output quantities of which (φmeas,filtp, Fmeas,filtp) are sent to a first multiplication module (16) for calculating a quotient Q=Fmeas,filtp/φmeas,filtp, connected downstream of the latter is a second multiplication module (17) in which the filtered value of the clamping force (Fmeas,filt) is divided by the quotient Q, and connected downstream of which is an addition module (18) in which the assessed value (φ0,assess) of the actuator position is calculated according to the formula (φ0,assess=φmeas,filt−Fmeas,filt/Q).