Eberhard P. Hofer

Analysis of the dynamics in microactuators using high-speed cine photomicrography

This paper discusses the visualization of microdevice dynamics using high-speed cine photomicrograph. The visualization results in image sequences, which contain the kinematic position data of the moving parts in a microsystem. Utilizing a mathematical model, it is shown in this paper how to extract information about the forces and torques acting on the microdevice. Furthermore, the values of system parameters can be calculated if a dynamic model of the process is available and the identification of the parameters is unambiguous. In this paper, the model-based evaluation of high-speed-cinematographic image sequences is demonstrated for a microturbine and a microrelay. The measurements on the microturbine have been performed with a setup, which allows an image frequency up to 100 million frames per second for nonreproducible processes. The measurements of the microrelay have been taken with a second experimental setup using the stroboscopic principle. In the case of the microrelay, the complete identification of the dynamic model used by us is carried out. A first application of our identified model is the design of an optimal current pulse for the microrelay to damp oscillations.

Diamond micro system for bio-chemistry

This work illustrates the potential of diamond micro system technologies progressively developed in the last years for an application in the bio-chemical field. A diamond micro reactor system based on a novel integration concept is presented and the role of diamond in this generic system is described. It consists of reaction chambers with removable bottom and integrated micro dosage elements allowing the ejection and mixture of two different fluids onto the removable bottom substrate. As an example, this system is used in a novel DNA-synthesis cycle. In this application the diamond micro reactor system combined with a specifically designed chemistry for the DNA-synthesis enables the parallel production of DNA-chain-clusters with individual sequence arranged in an array (DNA-Chip).

Thermal ink jet dynamics: modeling, simulation, and testing ☆

Abstract In this paper, we present a cinematographic measuring technique for visualization and characterization of dynamics in micro electro mechanical systems for the example of a thermal ink jet printhead. Furthermore, we derive a model for identification and simulation of dynamic phenomena in the thermal pneumatic microactuator of a thermal ink jet. Using this model we calculate the pressure propagation in the bubble by identifying the mathematical model with position measurements extracted from cinematographic image sequences which have been taken with our visualization equipment. The identification of the model was performed with minimizing the sum of quadratic deviations between simulated and measured values. Parameter studies with the identified model predict the behavior of the microactuator at outer pressures higher than 1 bar.

Interval methods for simulation of dynamical systems with state-dependent switching characteristics

In this paper, an interval arithmetic simulation algorithm is introduced for simulation of continuous-time systems with state-dependent switching between different dynamical models. For that purpose, the conditions for all possible transitions between these models have to be evaluated during simulation to determine the switching times and hence to obtain guaranteed enclosures for all state variables. In contrast to other simulation techniques, all system parameters are defined as interval variables to analyze the effect of uncertainties on the switching times and the dynamical behavior of the complete system

Disturbance estimation and compensation for trajectory control of an overhead crane

This paper presents an observer based control concept for an overhead crane using feedforward and feedback controllers. All control system components have been derived in symbolic form. Therefore, gain scheduling can be utilized to take into account varying system parameters. According to a decentralized control structure, a multibody model is presented for the crane y-axis and the equations of motion are stated. Based on a linearized state space representation, a feedback control law is calculated analytically. The feedforward control design and observer based disturbance rejection are described in detail due to their importance concerning tracking accuracy. The nonlinear friction force acting on the trolley drive and disturbance force acting on the load surface are considered. The effectiveness of the developed control scheme is shown by selected experimental results at a 5t-bridge crane.

Crane automation by decoupling control of a double pendulum using two translational actuators

Modeling a crane as a double pendulum enables control of the position as well as the tilt of the load. Using the trolley motion and an additional translational actuator at the load suspension unit as system inputs, a control structure is described, that achieves damping of sway and tilt oscillations and establishes a decoupling between position and tilt angle of the load. These control features are the foundation for using the crane as a large workspace covering robot with six degrees of freedom. State space methods are used to design the decoupling control. Experimental results on a 5 ton bridge crane with workspace dimensions of 30 m/spl times/9 m/spl times/7 m show the performance of the presented concept.

The Artificial Muscle as an Innovative Actuator in Rehabilitation Robotics

Abstract This paper presents the application of artificial pneumatic muscle actuators in a novel motorized orthosis for an intensive home-based gait training in patients with neurological disorders. Owing to the inherent elasticity of these actuators, they are an ideal choice in realizing a soft and tractable assistance to aid the physiological movements of the lower extremities. Special focus is paid to the modeling of the dynamic nonlinear force characteristics of the muscles as a steerable mass-damper system, and to the approximation of the variation of muscle volume under different operating conditions. The model description uses polynomial functions for which coefficients are identified by minimizing a quadratic performance index. Based on the mechanical model of the knee joint of the apparatus, a nonlinear stability-oriented backstepping control supported by observer-based disturbance compensation is derived and applied to the prototype of the rehabilitation robot.

Simulation of controlled uncertain nonlinear systems

In this paper a new method for the simulation of uncertain nonlinear discrete time systems is given. The problem of simulation is reformulated as an optimization problem. Using methods of global optimization, namely, interval analysis, the global solution to the optimization problem stated is computed. Derivatives of the objective function of the optimization problem are computed using methods of automatic differentiation. The presented approach is implemented on a SPARC Station using the language PASCAL-XSC. For a typical example simulation results are presented and discussed.

Derivation of Physically Motivated Constraints for Efficient Interval Simulations Applied to the Analysis of Uncertain Dynamical Systems

Derivation of Physically Motivated Constraints for Efficient Interval Simulations Applied to the Analysis of Uncertain Dynamical Systems Interval arithmetic techniques such as ValEncIA-IVP allow calculating guaranteed enclosures of all reachable states of continuous-time dynamical systems with bounded uncertainties of both initial conditions and system parameters. Considering the fact that, in naive implementations of interval algorithms, overestimation might lead to unnecessarily conservative results, suitable consistency tests are essential to obtain the tightest possible enclosures. In this contribution, a general framework for the use of constraints based on physically motivated conservation properties is presented. The use of these constraints in verified simulations of dynamical systems provides a computationally efficient procedure which restricts the state enclosures to regions that are physically meaningful. A branch and prune algorithm is modified to a consistency test, which is based on these constraints. Two application scenarios are studied in detail. First, the total energy is employed as a conservation property for the analysis of mechanical systems. It is shown that conservation properties, such as the energy, are applicable to any Hamiltonian system. The second scenario is based on constraints that are derived from decoupling properties, which are considered for a high-dimensional compartment model of granulopoiesis in human blood cell dynamics.

Interval Observer Design Based on Taylor Models for Nonlinear Uncertain Continuous-Time Systems

In most applications in control engineering not all state variables can be measured. Consequently, state estimation is performed to reconstruct the non-measurable states taking into account both system dynamics and the measurement model. If the system is subject to interval bounded uncertainties, an interval observer provides a guaranteed estimation of all states. The estimation consists of a recursive application of prediction and correction steps. The prediction step corresponds to a verified integration of the system model describing the system dynamics between two points of time at which measured data is available. In this paper, a Taylor model based integrator is used. Considering the state enclosures obtained in the prediction step, the correction step reconstructs states and parameters from the uncertain measurements with the help of a measurement model. The enclosures of states and parameters determined by the interval observer are consistent with both system and measurement models as well as all uncertainties.