Morten Bisgaard

Modeling of Generic Slung Load System

This paper presents the result of modelling and verification of a generic slung load system using a small-scale helicopter. The model is intended for use in simulation, pilot training, estimation, and control. The model is derived using a redundant coordinate formulation based on Gauss’ Principle of Least Constraint using the Udwadia-Kalaba equation and can be used to model all body to body slung load suspension types. The model gives an intuitive and easy-to-use way of modelling and simulating dierent slung load suspension types and it includes detection and response of wire slacking and tightening, and aerodynamical coupling between the helicopter and the load. Furthermore, it is shown how the model can be easily used for multi-lift systems either with multiple helicopers or multiple loads. A numerical stabilisation algorithm as well as a trim algorithm is presented for the complete helicopter/load system and finally the use of the model is illustrated through simulations.

Robust helicopter stabilization in the face of wind disturbance

When a helicopter is required to hover with minimum deviations from a desired position without measurements of a persistent wind disturbance, a robustly stabilizing control action is vital. In this paper, the stabilization of the position and translational velocity of a nonlinear helicopter model affected by a wind disturbance is addressed. The wind disturbance is assumed to be a sum of a fixed number of sinusoids with unknown amplitudes, frequencies and phases. An estimate of the disturbance is introduced to be adapted using state measurements for control purposes. A nonlinear controller is then designed based on nonlinear adaptive output regulation and robust stabilization of a chain of integrators by a saturated feedback. Simulation results show the effectiveness of the control design in the stabilization of helicopter motion and the built-in robustness of the controller in handling parameter and model uncertainties.

Development of a typing system for epidemiological studies of porcine toxin-producing Pasteurella multocida ssp. multocida in Denmark

The aim of the present study was to evaluate capsular-typing, plasmid-profiling, phage-typing and ribotyping for epidemiological studies of toxin-producing Pasteurella multocida ssp. multocida in Denmark. The evaluation of methods was based on 68 strains from nasal swabs and 14 strains from pneumonic lungs. Strains from lungs were all of capsular Type A, whereas strains from nasal swabs were of both capsular Types A and D. Only 9% of the strains contained plasmids, which could not be associated with antibiotic resistance. Phage-typing divided 61% of strains into 10 groups, while 39% were non-typable. CfoI ribotyping divided strains into four groups of which one type contained 94% of isolates. HindIII ribotyping divided strains into 18 types. A total of 18 strains from The Netherlands, UK and USA were subjected to HindIII ribotyping, resulting in 13 types of which six were identical to ribotypes of Danish strains. Phage-typing of isolates from an outbreak of atrophic rhinitis involving six herds in 1985 showed the existence of an epidemic strain. This type was recognised in the herd suspected of being the source of the infections and in four of the five infected herds. These findings were supported by HindIII ribotyping, as 85% of isolates from all herds were assigned to one ribotype. In conclusion, HindIII ribotyping seems to represent a useful tool for epidemiological studies of toxigenic P. multocida ssp. multocida.

Swing Damping for Helicopter Slung Load Systems using Delayed Feedback

of a swing reducing controller for helicopter slung load systems using intentional delayed feedback. It is intended for augmenting a trajectory tracking helicopter controller and thereby improving the slung load handing capabilities for autonomous helicopters. The delayed feedback controller is added to actively reduce oscillations of the slung load by improving the damping of the slung load pendulum modes. Furthermore, it is intended for integration with a feedforward control scheme based on input shaping for concurrent avoidance and dampening of swing. The design of the delayed feedback controller is presented as an optimization problem which gives the possibility of an automated design process. Simulations and ight test verications of the control system on two dierent autonomous helicopters are presented and it is shown how a signicant improvement of oscillation damping can be achieved.

Educational value and lessons learned from the AAU-CubeSat project

In September 2001 Aalborg university started the AAU-cubesat project that reached it climax when the student built satellite was launched into space on the 30th of June 2003 on top of a former Russian ICBM. AAU-cubesat was among the first five satellites to be launched that are built within the cubesat concept that prescribes a satellite with dimensions 10/spl times/10/spl times/10 cm and mass one kilogram. These constraints clearly limits the possibilities for the satellite in terms of possible scientific missions, but on the other hand: by building satellites of this size a technology push is created that in the future will help to reduce the size of both scientific and commercial satellites and thus help to drive down the launch cost. In this paper described the overall architecture of the AAU-cubesat in order to show what a pico-satellite can be and demonstrate all the fields of engineering which must come together to built a student satellite like the AAU-cubesat. Results from the operation phase will be stated, and recommendations on further work on pico-satellite designs will be given. In addition as the project has been carried through by students then the educational value of the project will be addressed as well.

VISION AIDED STATE ESTIMATOR FOR HELICOPTER SLUNG LOAD SYSTEM

Abstract This paper presents the design and verification of a state estimator for a helicopter based slung load system. The estimator is designed to augment the IMU driven estimator found in many helicopter UAVs and uses vision based updates only. The process model used for the estimator is a simple 4 state acceleration driven pendulum. Sensor input for the filter is provided by a vision based system that measures the position of the slung load. The estimator needs no prior knowledge of the system as it estimates the length of the suspension system together with the system states. Finally the estimator is verified using flight data and it is shown that it is capable of reliably estimating the slung load states.

Full State Estimation for Helicopter Slung Load System

This paper presents the design of a state estimator system for a generic helicopter based slung load system. The estimator is designed to deliver full rigid body state information for both helicopter and load and is based on the unscented Kalman filter. Two dierent approaches are investigated: One based on a parameter free kinematic model and one based on a full aerodynamic helicopter and slung load model. The kinematic model approach uses acceleration and rate information from two Inertial Measurement Units, one on the helicopter and one on the load, to drive a simple kinematic model. A simple and eective virtual sensor method is developed to maintain the constraints imposed by the wires in the system. The full model based approach uses a complex aerodynamical model to describe the helicopter together with a generic rigid body model. This rigid body model is based on a redundant coordinate formulation and can be used to model all body to body slung load suspension systems. Both estimators include bias estimation for the accelerometers and gyros and the model based estimator furthermore includes estimation of external wind disturbances. A vision system is used to measure the motion of the load relative to the helicopter. A method is devised to reduce the execution time of the process model in the unscented Kalman filter. The two approaches are tested through simulation and compared. The full model based approach shows better results than the kinematic model aproach, but at the cost of a larger computational burden.

The AAU-Cubesat Student Satellite Project: Architectural Overview and Lessons Learned

Abstract In September 2001 Aalborg university started the AAU-cubesat projectthat reached its climax when the student built satellite was launched into space on the 30th of June 2003 on top of a former Russian ICBM. AAU-cubesat was among the first five satellites to be launched that are built within the cubesat concept that prescribes a satellite with dimensions 10x10x10cm and mass one kilogram. This paper will describe the overall architecture of the AAU-cubesat in order to show what a pico-satellite can be and demonstrate all the fields of engineering which must come together to built a student satellite like the AAU-cubesat. Results from the operation phase will be stated, and recommendations on further work on pico-satellite designs will be given. In addition as the project has been carried through by students, the educational value of the project will be adressed as well.

Nonlinear feedforward control for wind disturbance rejection on autonomous helicopter

This paper presents the design and verification of a model based nonlinear feedforward controller for vertical and horizontal wind disturbance rejection on autonomous helicopters. The feedforward control is based on a helicopter model that is derived using a number of carefully chosen simplifications to make it suitable for the purpose. The model is inverted for the calculation of rotor collective and cyclic pitch angles given the wind disturbance. The control strategy is then applied on a small helicopter in a controlled wind environment and the effectiveness and advantage of the feedforward controller is demonstrated through flight tests.

Disturbance effects in nonlinear control systems and feedforward control strategy

This work concerns the development of a feedforward control strategy for measurable disturbance rejection in general nonlinear systems with feedback control. In other words, a separate design of disturbance feedforward controller is carried out to be augmented to an existing nonlinear feedback control system. With reference to a well known disturbance feedforward control of linear systems, feedforward control problem for general nonlinear control systems is formulated. The notion of disturbance effect is introduced with the aid of Lyapunov stability analysis of an asymptotically stable disturbance free nonlinear system with feedback control. With the establishment of the disturbance effect description, a feedforward control scheme that guarantees asymptotic stability in the presence of external disturbance is proposed and verified using the inverted pendulum system as an illustrative example.