Mechatronic design of direct drive systems

In contrast to conventional drives, with direct drives the motor is not created until it is integrated into the machine. The mechanical and electrical subsystems are merged to form the mechatronic system by the velocity and position control loops. Since control parameters have a crucial influence on the behavior of the complete system, a main goal of this article is to explain their importance for machine characteristics such as stiffness and dynamics. The disturbance behavior of directly driven systems is discussed in detail. Using the balance theorem, it is shown why an increase in stiffness gained by control in one frequency spectrum is always interconnected with a loss of stiffness for other frequencies. A finite element model of a roll serves to explain the modeling approach for directly driven machines and to show how the system stiffness can be increased by a proper choice of the encoder position.