Philipp Rapp

Nonlinear adaptive and tracking control of a pneumatic actuator via immersion and invariance

The present publication is focussed on the application of the immersion and invariance (I&I) control methodology on a pneumatic actuator. The utilization of I&I for tracking control is investigated and a tracking theorem is explicitly provided and proved. Based on this theorem, a tracking controller for the nonlinear system is designed. Furthermore, in order to deal with unknown parameters, we state and prove an adaptive tracking theorem. Using this theorem, the designed controller is extended in order to be able to estimate the current friction force. This renders the controller adaptive and enhances its tracking capability. Simulations as well as measurement results show the excellent performance of the adaptive I&I tracking controller.

An immersion and invariance based speed and rotation angle observer for the ball and beam system

The present contribution introduces a nonlinear observer for the rotation angle and the velocities of the ball and beam system. It is based upon the Immersion and Invariance (I&I) methodology and it uses measurements of the relative rotation angle and the absolute ball position. Significant practical relevance of this contribution is due to the relative rotation angle measurement, provided by most commercially available encoders. Observability of the system is studied and the nonlinear observer is designed using the (reduced-order) observer theorem of the I&I technique. The asymptotical convergence of the observation error is proved by means of Lyapunov arguments. Simulation experiments illustrate the theory and show the effectiveness of the proposed design.

Regression methods for ophthalmic glucose sensing using metamaterials

We present a novel concept for in vivo sensing of glucose using metamaterials in combination with automatic learning systems. In detail, we use the plasmonic analogue of electromagnetically induced transparency (EIT) as sensor and evaluate the acquired data with support vector machines. The metamaterial can be integrated into a contact lens. This sensor changes its optical properties such as reflectivity upon the ambient glucose concentration, which allows for in situ measurements in the eye. We demonstrate that estimation errors below 2% at physiological concentrations are possible using simulations of the optical properties of the metamaterial in combination with an appropriate electrical circuitry and signal processing scheme. In the future, functionalization of our sensor with hydrogel will allow for a glucose-specific detection which is insensitive to other tear liquid substances providing both excellent selectivity and sensitivity.

Performance study for an acoustic-inertial close range navigation system used in minimally-invasive surgical interventions

The present contribution is concerned with the design of a 3D real-time navigation system for minimally-invasive surgical interventions. We employ an absolute positioning system based on short range acoustic positioning technology together with an inertial navigation system. Both of the signals are fused using hybrid extended Kalman filtering in order to obtain a precise pose estimation of the surgical instrument. Simulation studies provide specification of the demands for the acoustic sensor system and the margins of usability for such a surgical navigation system.

Characterization of a 6 DOF acoustic-inertial navigation system for minimally-invasive surgery

A highly accurate 6 DOF real-time navigation system for minimally-invasive surgical interventions is presented. The system consists of short range acoustic transducers that combine time-of-flight and carrier-phase measurements and a standard inertial measurement unit. With Hybrid Extended Kalman Filtering, a precise pose estimation of the surgical instrument is achieved. In this contribution, simulation results focussing on different noise variances, which are experimentally obtained from a prototype setup, and initial errors are presented. In addition to previous work, the main advance lies in the estimate of the orientation of the laparoscopic instrument through the use of multiple acoustic transducers.

A concept for a novel surgical navigation system

A new concept for surgical navigation in minimally-invasive interventions is presented, which allows an enhanced orientation of the surgeon with reduced cost and system complexity. The navigation system takes advantage of recorded image data, including the preoperatively computed tomography (CT) and magnetic resonance tomography (MRT) data, which are registered and segmented in order to obtain relevant biological markers, as well as the intraoperative camera data. A device for absolute positioning, included in the laparoscope and consisting of an acoustic indoor localization with a supporting inertial measurement unit (IMU), fuses these different navigation data for reliable 6 degree-of-freedom (DOF) position and orientation estimation. With those navigation information of the laparoscope, the landmarks of the preoperative data are localized on the intraoperative camera images via augmented reality and thus the site of the relevant features (e. g., a carcinoma) is determined.

Valve flow rate identification and robust force control for a pneumatic actuator used in a flight simulator

The present contribution deals with the development of a robust force controller for a pneumatic actuator that is employed in a flight simulator. Established control design techniques that deal with parametric uncertainties are applied and yield a control law which is tuned on a Rapid Control Prototyping system and implemented on a low-cost embedded system. The controller performance is evaluated for both systems using a test rig. Special emphasis regarding the experimental results is put on the effect of feedforward control in combination with offline trajectory generation. On top of that, a new concept for valve conductance identification is presented in this contribution. The novel approach reduces both computational expense and the effect of noise in analog sensors and outperforms the direct evaluation of the pressure dynamics equation.

Gramian-based actuator placement with spillover reduction for active damping of adaptive structures

Adaptive structures are engineering structures with the ability to modify their response to external loads. This includes active damping of externally induced vibrations. The controller design is usually based on reduced order models that comprise the most important vibration modes of the structure. This can lead to unwanted excitation of the neglected modes, known as control spillover. One means to cope with this problem is by proper placement of the actuators. In this contribution, we present a method for optimal actuator placement for active damping of adaptive structures that explicitly considers spillover effects by optimizing the trade-off between controllability of the considered and neglected modes. The optimization criterion is based on the controllability Gramian. Under certain conditions, the globally optimal solution can be found. The proposed method is applied to a numerical example of a high-rise truss structure.

Opto-acoustic distance measurement using spread spectrum techniques and carrier phase measurements

In this contribution, a novel opto-acoustic indoor navigation system for linear distance measurement is presented. The novelty consists in the simultaneous use of envelope time-of-flight (ETF) and carrier phase (CPH) measurements. In particular, we establish a two-channel link consisting of an ultrasound and infrared channel, the latter using a carrier frequency equal to the ultrasound frequency. In order to render the system extendible for multiple transmitters and receivers, code-division-multiple-access using Gold codes is employed, as all ultrasound and infrared signals share the same carrier frequency. This is also beneficial for multipath scattering suppression. The time difference between the carrier phase of the received ultrasound and infrared signals offers a high resolution but ambiguous distance signal. On the other hand, correlation of the received signals yields a coarse but unique distance signal. Experimental results show that a measurement resolution in the submillimeter range is feasible.

An immersion and invariance based speed and rotation angle observer for a class of revolute/prismatic manipulators with two degrees of freedom

This contribution presents a nonlinear observer for a class of revolute/prismatic (RP) manipulators with two degrees of freedom. It is based upon the Immersion and Invariance (I&I) methodology and uses measurements of the revolute joints relative angle and the prismatic joints absolute position. The estimated quantities consist of the absolute rotation angle as well as the linear and angular velocities. The practical relevance of this contribution is given by the processing of the relative rotation angle measurement, provided by most commercially available encoders. For the considered system class the observability is studied and a nonlinear observer is designed using the (reduced-order) observer theorem of the I&I technique. Employing Lyapunov arguments, the asymptotical convergence of the observation error is proven.