Abstract: A method for actuating an electric motor for a rheometer includes transferring drive energy to a sample. A time profile for deflection is periodic, a value for deflection is a measured variable, the motor is actuated by a manipulated variable, the measured and manipulated variables are mutually nonlinear, an approximation function for the time profile is a weighted sum of base functions, weights for base functions are a parameter vector, the manipulated variable is a weighted sum of base functions. The measured variable is sampled, sampled values are used within a time window, an approximation function for sampled values is a weighted sum of base functions, the weights are an actual parameter vector, a difference between intended and actual parameter vectors is subtracted from the manipulated parameter vector, the manipulated variable is a weighted sum of base functions and values of a new manipulated parameter vector are used as weights.