Adaptive compensation of torque disturbances and beyond

This paper addresses the problem of adaptive compensation of torque disturbances in the tracking/positioning control of mechanical systems with the aim of (1) reducing the tracking error for tracking and the position error for positioning tasks, (2) increasing the robustness for uncertain parameters, and (3) using the estimated parameters for failure detection/determination and wear indication. The compensation is incorporated in a standard adaptive nonlinear controller. It merges structural torque disturbance compensation that is important for high velocities and low velocity friction compensation. The stability of the closed loop control system is assessed. The control scheme proposed is applied and tried out on a simulation model and an experimental system. The results indicate that the compensation method proposed is viable, and the degree of verisimilitude of the compensation model is high enough to enable us to use the values of the adapted model parameters for failure detection/determination and wear indication. The last point, however, requires still some experimental evidence. It is expected that the method proposed is suitable for implementation on industrial robots, both for accurate tracking/positioning tasks alone as possibly combined with failure detection/determination. The method is not expected to perform well in the presence of large unmodeled dynamics, i.e., for mechanical systems with flexible joints or with flexible links, e.g., for space structures, without further modification

The use of acceleration measurements to improve the tracking control of robots

The paper discusses the use of acceleration measurements to improve the performance and robustness of controllers for robotic systems. There are at least two approaches: 1) direct use of the acceleration in a feedback loop to improve the performance and robustness, and 2) indirect use in an observer to improve the estimates of position and speed of the robot. An evaluation of both approaches is presented, using simulations and experiments on a flexible multi degree-of-freedom XY-table. Several proposals for the use of acceleration in the feedback loop, giving slightly modified controllers, are discussed. The design of the controllers is based on a simplified two degree-of-freedom model. The observer is of the predictive type to compensate for the time delay in the implementation, and its design is partially based on the Kalman filter theory. The simulation and experimental results enable us to draw some conclusions with respect to the improvement of performance and robustnes

Input/output selection for planar tensegrity models

A systematic method of selecting sensors and actuators is produced, efficiently selecting inputs and outputs that guarantee a desired level of performance in the ∞-norm sense. The method employs an efficiently computable necessary and sufficient existence condition, using an effective search strategy. The search strategy is based on a method to generate all so-called minimal dependent sets. This method is applied to tensegrity structures. Tensegrity structures are a prime example for application of techniques that address structural problems, because they offer a lot of flexibility in choosing actuators/sensors and in choosing their mechanical structure. The selection method is demonstrated with results for a 3 stage planar tensegrity structure where all 26 tendons can be used as control device, be it actuator, sensor, or both, making up 52 devices from which to choose. In our set-up it is easy to require devices to be selected as colocated pairs, and to analyze the performance penalty associated with this restriction. Two performance criteria were explored, one is related to the dynamical stiffness of the structure, the other to vibration isolation. The optimal combinations of sensors and actuators depend on the design specifications and are really different for both performance criteria

Combustion and noise phenomena in turbulent alkane flames

A gas turbine engine is an advanced apparatus for propulsion and power generation that has been developed over the last 60 years. The energy for this production\ud of propulsion and power in a gas turbine is generated by combustion.\ud It is feasible and relatively easy to solve the governing equations in combustion for one dimensional laminar hydrocarbon combustion with detailed chemistry. This has been done for several hydrocarbon fuels that are representative for liquid fuel combustion. The complex chemistry that is solved completely in a laminar flame is mostly modelled in simulations of turbulent combustion. Essential to this modelling is a correct understanding of the processes that govern the chemistry. Via the route of a numerical perturbation method, the CSP-method, this understanding can be developed. After analysis with CSP, the next step to a model describing turbulent combustion in gas turbines is taken using the CFI combustion model. This model comprises the definition of a reaction progress variable representing the reduced chemistry yielding from CSP, a mixture fraction variable and an enthalpy variable. The thesis presents a version of the CFI combustion model for application in evaporating fuel sprays

Powertrain sizing of electrically supercharged internal combustion engine vehicles

We assess the concept of electrically supercharged internal combustion engines, where the supercharger, consisting of a compressor and an electric motor, draws electric power from a buffer (a battery or a supercapacitor). In particular, we investigate the scenario of downsizing the engine, while delivering high power demands by supercharging. Simultaneously, we seek the optimum buffer size that provides sufficient electric power and energy to run the supercharger, such that the vehicle is able to deliver the performance required by a driving cycle representing the typical daily usage of the vehicle. We provide convex modeling steps that formulate the problem as a second order cone program that not only delivers the optimal engine and buffer size, but also provides the optimal control and state trajectories for a given gear selection strategy. Finally, we provide a case study of sizing the engine and the electric buffer for different compressor power ratings

Combining extremum seeking control and tracking control for high-performance CVT operation

Abstract—The control design for the variator in a pushbelt continuously variable transmission (CVT) is investigated. The variator enables a stepless variation of the transmission ratio within a finite range. A conventional variator control design is typically obtained by the use of a variator model, which is highly uncertain and, therefore, limits the variator efficiency. In this paper, a variator control design is proposed, which simultaneously satisfies the variator control objectives: 1) track-ing a transmission ratio reference, 2) optimizing the variator efficiency. Furthermore, the variator control design, which con-sists of a combination of extremum seeking control (ESC) and tracking control (TC), only uses measurements from sensors that are standard. Experiments illustrate that the variator control design achieves the variator control objectives and show that a conventional variator control design is outperformed. I

Selectivity of F-18-FLT and F-18-FDG for differentiating tumor from inflammation in a rodent model

Increased glucose metabolism of inflammatory tissues is the main source of false-positive F-18-FDG PET findings in oncology. It has been suggested that radiolabeled nucleosides might be more tumor specific. Methods: To test this hypothesis, we compared the biodistribution of 3'-deoxy-3'-F-18-fluorothymidine (FLT) and F-18-FDG in Wistar rats that bore tumors (C6 rat glioma in the right shoulder) and also had sterile inflammation in the left calf muscle (induced by injection of 0.1 mL of turpentine). Twenty-four hours after turpentine injection, the rats received an intravenous bolus (30 MBq) of either F-18-FLT (n = 5) or F-18-FDG (n = 5). Pretreatment of the animals with thymidine phosphorylase (>1,000 U/kg, intravenously) before injection of F-18-FLT proved to be necessary to reduce the serum levels of endogenous thymidine and achieve satisfactory tumor uptake of radioactivity. Results: Tumor-to-muscle ratios of F-18-FDG at 2 h after injection (13.2 +/- 3.0) were higher than those of F-18-FLT (3.8 +/- 1.3). F-18-FDG showed high physiologic uptake in brain and heart, whereas F-18-FLT was avidly taken up by bone marrow. F-18-FDG accumulated in the inflamed muscle, with 4.8 +/- 1.2 times higher uptake in the affected thigh than in the contralateral healthy thigh, in contrast to F-18-FLT, for which this ratio was not significantly different from unity (1.3 +/- 0.4). Conclusion; In F-18-FDG PET images, both tumor and inflammation were visible, but F-18-FLT PET showed only the tumor. Thus, the hypothesis that F-18-FLT has a higher tumor specificity was confirmed in our animal model