Signal analysis and system identification of an active mechanical lung simulator in order to design a control regime

Abstract

In modern medicine simplified mechanical or mathematical substitute models of the human body has become an effective method for analyzing processes, estimating parameters for diagnostic purposes and performing simulations. Active mechanical models of respiratory systems are consulted to train clinicians and medical staff as well as to optimize ventilator soft- and hardware. To provide a realistic scenario it is important to create a system that behaves as similar as possible to the physiological respiratory tract. Therefore a novel concept for active mechanical lung simulation was developed. The design is based on a cylinder-pistonsystem employing an electromagnetic linear motor. Roll membranes are used for sealing allowing for smooth movement with low inner friction. For such a new system it is necessary to analyze the transfer behavior in order to develop an appropriate control system. To determine the transfer function of the system, the frequency response for different motor positions was used. For calculating amplitude and phase responses, the measured sinusoidal signals were approximated using a leastsquares approach. Based on the calculated values, Bode diagrams were derived. As the Bode diagrams for all measured positions were comparable, it can be assumed that the transfer behavior over the whole piston travel range is constant. Hence, one transfer function was determined by means of system identification that can now be used as a basis for designing the control regime. This method represents an effective procedure to design a precise regime and makes it possible to design this new type of a realistic lung simulator.