A study of viscous frictional effects and relay characteristics on the operation of a positional relay servomechanism

The thesis describes some experimentally observed data and analytical approaches to the study of a relay servomechanism. The experimental data were secured from an analog simulation of a relay servo system. The results of this data were compared to the transient approach by use of the phase-plane method. The stability of the system was determined using a describing-function. The analytical approaches are described in the presentation. A study of the effects of viscous friction is described, and the characteristic of the relay used in the system is given special attention. The response to input driving function was considered, and rise time, overshoot, settling time and steady state errors were considered as important criteria for determining the over-all performance. Finally, a recommendation is given as to the approach to the synthesis and analysis of a relay servomechanism --Abstract, page 2

Automatic Tuning of PID Controllers Based on Asymmetric Relay Feedback

This thesis presents an improved version of the classic relay autotuner. The proposed autotuner uses an asymmetric relay function to better excite the process in the experiment phase. The improved excitation provides the possibility to obtain better models and hence better tuning, without making the autotuner more complicated or time consuming.Some processes demand more accurate modeling and tuning to obtain con-trollers of sufficient performance. The proposed autotuner can classify these processes from the experiment. In an advanced version of the autotuner an additional experiment could be dhttps://localhost/admin/login.phpesigned for these processes, in order to further increase the possibilities in modeling and tuning. The experiment design would then rely on information from the relay experiment. A simple version of the autotuner could instead make a somewhat better model estimation immediately, or suggest that some extra effort may be put in modeling if the control performance of the loop is crucial. The main focus in this thesis is on the simple version of the autotuner.The proposed autotuner uses the process classification for model and controller selection also in the simple version. The processes are classified according to their normalized time delays. In this thesis a simple method of finding the normalized time delay from the asymmetric relay experiment is presented and evaluated.Research presented on different versions of the relay autotuner is often based solely on simulations. In large simulation environments, the ability to automatically tune the large amount of PID controllers is practical and time-saving. However, the ability to use the autotuner in an industrial setting, requires considerations not always present in a simulation environment. This thesis investigates many of these issues, regarding parameter settings and possible error sources. The proposed autotuner is implemented, tested and evaluated both in a simulation environment and by industrial experiments. The simple version of the autotuner gives satisfactory results, both in simulations and on the industrial processes. Still, there is a possibility to further increase the performance by an advanced version of the autotuner

Identifikacija bespilotnih ronilica korištenjem postupka vlastitih oscilacija

Control of underwater vehicles is a challenging task since these systems demonstrate highly coupled and nonlinear behavior in uncertain and often unknown environment. In order to successfully design higher levels of control hierarchy, sufficiently accurate parameters of a mathematical model describing the vessel is required. These parameters vary significantly depending on the payload; hence conventional, time-consuming identification methods are tedious. This paper introduces a self-oscillation based method for determining inertia and drag parameters for underwater vehicles. The procedure is easily implementable in field conditions and gives satisfactory results. Both linear and nonlinear models of yaw, heave and surge degree of freedom can be identified. Experimental results obtained from yaw identification experiments on a real underwater vehicle will be presented. In addition to this, the same methodology will be used to determine which model describes the vehicle dynamics more suitably. Modifications of the proposed algorithm for systems with delays and discrete-time systems will be described, together with an estimate of parameter error bounds due to quantization levels.Upravljanje bespilotnim ronilicama predstavlja zahtjevan zadatak budući da ronilice pokazuju snažno spregnuto i nelinearno ponašanje u nepredvidljivim i često nepoznatim okruženjima. U svrhu uspješnog projektiranja viših razina u njihovoj upravljačkoj hijerarhiji, potrebno je dovoljno dobro poznavati parametre matematičkog modela plovila. Ovi se parametri mogu znatno mijenjati ovisno o opremi i drugim uvjetima tijekom misije, stoga su uobičajeni, vremenski zahtjevni identifikacijski postupci neprikladni. Članak opisuje postupak koji koristi vlastite oscilacije za određivanje inercije i otpornosti bespilotnih ronilica. Postupak je lako primjenjiv u terenskim uvjetima i daje zadovoljavajuće rezultate. Linearan i nelinearan model zaošijanja, zaranjanja i napredovanja mogu´ce je identificirati. U radu su prikazani eksperimentalni rezultati dobiveni na identifikacijskim ekperimentima zaošijanja na stvarnoj ronilici. Uz navedeno, ista metodologija je iskorištena za odlučivanje o modelu koji prikladno opisuje stvarnu ronilicu. U radu su opisane i preinake predloženog algoritma za sustave s transportnim kašnjenjem i diskretne sustave, kao i procjene pogrešaka u određivanju parametara koje su posljedica kvantizacije

Indirect approach to continuous time system identification of food extruder

A three-stage approach to system identification in the continuous time is presented which is appropriate for day-to-day application by plant engineers in the process industry. The three stages are: data acquisition using relay feedback; non-parametric identification of the system step response; and parametric model fitting of the identified step response. The method is evaluated on a pilot-scale food-cooking extruder

On stiffness and damping of vibro-impact dynamics of backlash

We consider the instantaneous stiffness and damping of the vibro-impact in a backlash pair. Opposed to the existing and mostly used models of the backlash, we address the problem of contact and separation, and the associated force propagation within a mechanical pair, from a viewpoint of the vibro-impact dynamics. We discuss the impact forces with the coefficient of restitution as a principal factor which shapes the transient backlash response.We show that a common approach to modeling the backlash by means of a dead-zone in a restoring force is unsuitable for correctly capturing the mechanical impact. We exemplary demonstrate a qualitative accord between an experimental backlash response and the postulated modeling approach. Backlash related energy losses by damping of vibro-impact system are also addressed in brief.acceptedVersio

Operational experience with the electronic flight control systems of a lunar-landing research vehicle

Operational performance of electronic flight control system for lunar landing research vehicle

A three-state clutch servomechanism for an underwater control surface.

Bibliography: p. 82.Based on an E.E. thesis in the Dept. of Electrical Engineering, 1968.Contract no. NOw-66-0178d. DSR Project no. 76094

Relay feedback systems - established approaches and new perspectives for application

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Hybrid modeling and control of mechatronic systems using a piecewise affine dynamics approach

This thesis investigates the topic of modeling and control of PWA systems based on two experimental cases of an electrical and hydraulic nature with varying complexity that were also built, instrumented and evaluated. A full-order model has been created for both systems, including all dominant system dynamics and non-linearities. The unknown parameters and characteristics have been identi ed via an extensive parameter identi cation. In the following, the non-linear characteristics are linearized at several points, resulting in PWA models for each respective setup. Regarding the closed loop control of the generated models and corresponding experimental setups, a linear control structure comprised of integral error, feed-forward and state-feedback control has been used. Additionally, the hydraulic setup has been controlled in an autonomous hybrid position/force control mode, resulting in a switched system with each mode's dynamics being de ned by the previously derived PWA-based model in combination with the control structure and respective mode-dependent controller gains. The autonomous switch between control modes has been de ned by a switching event capable of consistently switching between modes in a deterministic manner despite the noise-a icted measurements. Several methods were used to obtain suitable controller gains, including optimization routines and pole placement. Validation of the system's fast and accurate response was obtained through simulations and experimental evaluation. The controlled system's local stability was proven for regions in state-space associated with operational points by using pole-zero analysis. The stability of the hybrid control approach was proven by using multiple Lyapunov functions for the investigated test scenarios.publishedVersio

Linear Macro-Micro Positioning System Using a Shape Memory Alloy Actuator

The use of high-precision automated equipment is steadily increasing due in part to the progressively smaller sizes of electronic circuits. Currently, piezoelectric transducers (piezos) dominate as the actuation device for high precision machines, but shape memory alloys (SMA) may be a viable alternative to reduce monetary costs. This work explores the implementation of a low-cost linear macro-micro positioning system. The system consists of a modified printer carriage to provide long range, macro scale linear motion (approximately 200 mm range and 200 µm precision) and a micro scale system (approximately 4 mm range and 5 µm target precision) that uses an SMA actuator. A detailed description of the design and implementation of the system is given in this research. A model of the macro-stage is then generated by first identifying and inverting a simple friction model to linearize the system, thereby allowing for modified least squares (MLS) identification of a linear model. Various controllers are attempted for the macro-stage and compared with an experimentally tuned nonlinear PD controller that is implemented in the final design. A model of the micro-stage is derived through analysis of the SMA actuator. The model for the actuator is separated into two portions, an electro-thermal model, and a hysteresis model. The hysteresis model is derived using the Preisach model, and the electro-thermal model through MLS identification. To control the micro-stage, a PI controller with antiwindup is developed experimentally. The two stages are then executed together in closed loop and the resulting coupling between the two stages is briefly examined. Experimental data used for the modelling and design is presented, along with results of the final macro-micro linear positioning system