Mario Klünder

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.

Development of a pneumatically driven flight simulator Stewart platform using motion and force control

In this paper we develop a motion platform driven by pneumatic actuators for a flight simulator. The platform itself is a Stewart platform with an extra cylinder in the middle. To control the platform two control methods are proposed, with the benefit of eliminating the kinematic constraints caused by the seven-cylinders configuration. The six outer cylinders are controlled according to motion trajectories whereas the middle cylinder acts as a pure force actuator to lift the weight of the platform. The Immersion and Invariance method with an additional friction compensator is applied for motion control. The method of exact input/output linearization is used for controlling the lift force of the middle cylinder. The measurement results show that the proposed method is effective for controlling the platform.

High definition urethral pressure profilometry: Evaluating a novel microtip catheter

Urethral pressure profilometry (UPP) is used in the diagnosis of stress urinary incontinence (SUI). SUI is a significant medical, social, and economic problem, affecting about 12.5% of the population. A novel microtip catheter was developed for UPP featuring an inclination sensor and higher angular resolution compared to systems in clinical use today. Therewith, the location of each measured pressure sample can be determined and the spatial pressure distribution inside the urethra reconstructed. In order to assess the performance and plausibility of data from the microtip catheter, we compare it to data from a double balloon air charged system.

Towards a Treatment of Stress Urinary Incontinence: Application of Mesenchymal Stromal Cells for Regeneration of the Sphincter Muscle.

Stress urinary incontinence is a significant social, medical, and economic problem. It is caused, at least in part, by degeneration of the sphincter muscle controlling the tightness of the urinary bladder. This muscular degeneration is characterized by a loss of muscle cells and a surplus of a fibrous connective tissue. In Western countries approximately 15% of all females and 10% of males are affected. The incidence is significantly higher among senior citizens, and more than 25% of the elderly suffer from incontinence. When other therapies, such as physical exercise, pharmacological intervention, or electrophysiological stimulation of the sphincter fail to improve the patient’s conditions, a cell-based therapy may improve the function of the sphincter muscle. Here, we briefly summarize current knowledge on stem cells suitable for therapy of urinary incontinence: mesenchymal stromal cells, urine-derived stem cells, and muscle-derived satellite cells. In addition, we report on ways to improve techniques for surgical navigation, injection of cells in the sphincter muscle, sensors for evaluation of post-treatment therapeutic outcome, and perspectives derived from recent pre-clinical studies.

Signal processing in urodynamics: towards high definition urethral pressure profilometry

BackgroundUrethral pressure profilometry (UPP) is used in the diagnosis of stress urinary incontinence (SUI) which is a significant medical, social, and economic problem. Low spatial pressure resolution, common occurrence of artifacts, and uncertainties in data location limit the diagnostic value of UPP. To overcome these limitations, high definition urethral pressure profilometry (HD-UPP) combining enhanced UPP hardware and signal processing algorithms has been developed. In this work, we present the different signal processing steps in HD-UPP and show experimental results from female minipigs.MethodsWe use a special microtip catheter with high angular pressure resolution and an integrated inclination sensor. Signals from the catheter are filtered and time-correlated artifacts removed. A signal reconstruction algorithm processes pressure data into a detailed pressure image on the urethra’s inside. Finally, the pressure distribution on the urethra’s outside is calculated through deconvolution. A mathematical model of the urethra is contained in a point-spread-function (PSF) which is identified depending on geometric and material properties of the urethra. We additionally investigate the PSF’s frequency response to determine the relevant frequency band for pressure information on the urinary sphincter.ResultsExperimental pressure data are spatially located and processed into high resolution pressure images. Artifacts are successfully removed from data without blurring other details. The pressure distribution on the urethra’s outside is reconstructed and compared to the one on the inside. Finally, the pressure images are mapped onto the urethral geometry calculated from inclination and position data to provide an integrated image of pressure distribution, anatomical shape, and location.ConclusionsWith its advanced sensing capabilities, the novel microtip catheter collects an unprecedented amount of urethral pressure data. Through sequential signal processing steps, physicians are provided with detailed information on the pressure distribution in and around the urethra. Therefore, HD-UPP overcomes many current limitations of conventional UPP and offers the opportunity to evaluate urethral structures, especially the sphincter, in context of the correct anatomical location. This could enable the development of focal therapy approaches in the treatment of SUI.

Sampling lattice and signal reconstruction in urodynamics

Urethral pressure profilometry is a tool in the diagnosis of urinary incontinence. The pressure profile along the urethra is measured by a special catheter in order to asses the contraction strength of the sphincter muscle. However, the diagnostic value of pressure profilometry is limited. We seek to increase the diagnostic value by providing a detailed spatial reconstruction of the pressure profile on the surface of the urethra. Therefore, we investigate the sampling lattice (i.e., spatial sample distribution) and its properties with respect to signal reconstruction depending on the catheters sensor configuration and retraction motion. A sampling lattice with beneficial properties for reconstruction is generated through downsampling and a coordinate transformation of the original samples. We investigate its stability properties and present a reconstruction algorithm for the two-dimensional pressure distribution. Simulation results for signal reconstruction and stability properties conclude this work.

Precise injection of human mesenchymal stromal cells in the urethral sphincter complex of Göttingen minipigs without unspecific bulking effects

To investigate if injection of cells in the urethral sphincter complex causes unspecific bulking effects.

Eliminating pulse-induced artifacts in Urethral Pressure data.

Urethral Pressure Profilometry (UPP) is a tool in the diagnosis of urinary incontinence. The pressure profile along the urethra is measured by a special catheter in order to assess the contraction strength of the sphincter muscle. The use of microtip catheters with several pressure sensors and an integrated acceleration sensor enables signal reconstruction of the pressure distribution on the urethras inside. Experimental data from minipigs exhibit artifact patterns in the pressure data. It is shown that these artifacts are caused by vascular pulsation in the sphincter structure. We therefore investigate different methods exploiting the time-correlation of the artifacts to eliminate pulse-induced artifacts in the pressure data without compromising the actual signal. Evaluation of these methods applied to experimental data conclude this work showing that both an Input-Model and Principal Component Analysis Decorrelation are effective at removing the artifacts.

Assessing the reproducibility of high definition urethral pressure profilometry and its correlation with an air‐charged system

Recently, a new urodynamic method for the assessment of stress urinary incontinence called high definition urethral pressure profilometry (HD‐UPP) has been introduced. This method combines a novel microtip catheter with advanced signal processing to enable spatial data location and the reconstruction of a pressure image inside the urethra. In order to assess the reproducibility of HD‐UPP data, we statistically evaluate HD‐UPP datasets and compare them to data from a double balloon air‐charged system.

Using deconvolution to determine the sphincter strength distribution around the urethra

Urethral Pressure Profilometry (UPP) is a tool in the diagnosis of urinary incontinence. The pressure profile along the urethra is measured by a special catheter in order to assess the contraction strength of the sphincter muscle. However, the diagnostic value of pressure profilometry is limited. We seek to increase the diagnostic value by providing a detailed spatial reconstruction of the pressure profile on the outside surface of the urethra. We use deconvolution in order to solve the inverse problem of determining the pressure distribution on the outside of a tube from measured data on the inside. Therefore, we propose a parametric Point-Spread-Function (PSF) and optimize its parameters using a Finite-Element (FE) model. Simulation results verifying accuracy and robustness of this method conclude this work.