No description available.

no / A milk pasteurization process is a nonlinear process and multivariable interacting system. This makes it difficultly to control by the conventional on-off controllers. Even if the on-off controller can managed the milk temperatures in the holding tube and the cooling stage of the plate pasteurizer according to the plant's requirements, the dynamic profiles of the milk temperature are oscillating around a desired value. Consequently, this work is aimed at improving the control performance by a multi-variables control approach with model predictive control (MPC). The proposed algorithm was tested in the case of set point tracking under nominal condition gathered by the real observation. To compare the performance of the MPC controller, a model-based control approach of generic model control (GMC) coupled with cascade control strategy is taken into account. The simulation results demonstrated that a proposed control algorithm performed well in keeping both the milk and water temperatures at the desired set points without any oscillation and overshoot. Because of the predictive control strategy, the control response for MPC was less drastic control action compared to the GMC.

The concept of using heat flux measurements to provide the input for a feedforward temperature control loop is investigated. The feedforward loop is added to proportional and integral feedback control to increase the speed of the response to a disturbance. Comparison is made between the feedback and the feedback plus feedforward control laws. The control law with the feedforward control loop is also compared to the conventional approach of adding derivative control to speed up the system response to a disturbance. The concept was tested using a simple flat plate heated on one side and exposed to a step change in the convective heat loss on the other side. A controller was constructed using an analog computer to compare the feedforward and feedback approaches. The conventional control approach was tested using a commercial temperature controller. The feedback and feedforward approaches were also simulated. The results showed that the feedforward control approach produced significant improvements in the response to the disturbance. The integral of the squared error between the setpoint and actual temperature was reduced by approximately 90 percent by the addition of feedforward control to the feedback control. The maximum temperature deviation from the setpoint was also reduced by 70 percent with the addition of feedforward control. Qualitative agreement was obtained between the experimental results and the computer simulations. The conventional approach of adding derivative control to the proportional and integral control showed an increase of 20 percent in the integral of the squared error, but offered no significant improvement in the maximum temperature deviation. The addition of derivative control also caused the stability of the system to decrease, while the addition of feedforward had no adverse effects on the system stability. The concept of using heat flux measurements for feedforward control was successfully demonstrated by both simulations and experiments. / Master of Science

The Friction Stir Welding (FSW) process has been under constant developmentsince its invention, more than 20 years ago. Whereas most industrial applicationsuse a gantry machine to weld linear joints, there are applications which consistof complex three-dimensional joints, requiring more degrees of freedom fromthe machines. The use of industrial robots allows FSW of materials alongcomplex joint lines. There is however one major drawback when using robotsfor FSW: the robot compliance. This results in vibrations and insufficient pathaccuracy. For FSW, path accuracy is important as it can cause the welding toolto miss the joint line and thereby cause welding defects.The first part of this research is focused on understanding how welding forcesaffect the FSW robot accuracy. This was first studied by measuring pathdeviation post-welded and later by using a computer vision system and laserdistance sensor to measure deviations online. Based on that knowledge, a robotdeflection model has been developed. The model is able to estimate thedeviation of the tool from the programmed path during welding, based on thelocation and measured tool forces. This model can be used for online pathcompensation, improving path accuracy and reducing welding defects.A second challenge related to robotic FSW on complex geometries is thevariable heat dissipation in the workpiece, causing great variations in the weldingtemperature. Especially for force-controlled robots, this can lead to severewelding defects, fixture- and machine damage when the material overheats.First, a new temperature method was developed which measures thetemperature at the interface of the tool and the workpiece, based on the thermoelectriceffect. The temperature information is used as input to a closed-looptemperature controller. This modifies primarily the rotational speed of the tooland secondarily the axial force. The controller is able to maintain a stablewelding temperature and thereby improve the weld quality and allow joining ofgeometries which were impossible to weld without temperature control.Implementation of the deflection model and temperature controller are twoimportant additions to a FSW system, improving the process robustness,reducing the risk of welding defects and allowing FSW of parts with highlyvarying heat dissipation.

Temperature is a very important process parameter in Friction Stir Welding (FSW), but until lately active control of temperature has not been practiced. Recently, temperature control via a PID controller has proven to be effective. Model Predictive Control (MPC) is a control method that holds promise, but has not been attempted in FSW before. Two different model forms are developed for MPC and are evaluated. The first is a simple first-order plus dead time (FOPDT) model. The second is the Hybrid Heat Source model and is more complex; it combines the heat source method and a 1D discretized thermal model of the FSW tool. Model parameters were determined by fitting model predictions to actual weld data. The models were evaluated for their performance in modeled and unmodeled disturbances once the process was already at a quasi steady state condition and also were evaluated for control immediately after plunge. The FOPDT based MPC controller has very good performance and was comparable in performance to previously proven and well-tuned PID controllers. For small modeled disturbances the FOPDT controller settled within 1°C of the setpoint in 10s with almost no oscillations and only 2°C of overshoot. For large unmodeled disturbances, the FOPDT controller settled within 1°C of the setpoint in 30s with no oscillations and 16°C of overshoot. For the same disturbances, the PID servo controller settled in 30s with no oscillations and 9°C of overshoot, and the PID regulator controller settled in 15s but had almost a full oscillation and 13°C of overshoot.The Hybrid Heat Source MPC controller and the PID regulator controller were also able to control temperature within 5°C of the setpoint immediately after the plunge during the highly transient portion of the weld, which previously had been assumed to be too difficult to control. The PID regulator controller had a high degree of variability between the two runs (a settling time of 10s and 30s, and .5 and 4.5 oscillations before settling), but settled quickly and once settled was able to hold the temperature within 2°C of the setpoint. The HHS MPC controller on the other hand had far fewer oscillations (0 and 1 oscillation) before settling, but could only hold the temperature within 5°C of the setpoint. Both of these controllers performed far better than the FOPDT MPC and PID servo controllers.

Friction stir welding has become a popular forging technique used in many applications. The Swedish Nuclear Fuel and Waste Management Company (SKB) evaluates this method to seal the 5 cm thick copper canisters that will contain the spent nuclear fuel. To produce repetitive, high quality welds, the process must be controlled, and today a cascade controller is used to keep the desired stir zone temperature. In this thesis, the control system is extended to also include a plunge depth controller. Two different approaches are evaluated; the first attempt is a decentralized solution where the cascaded temperature controller is kept, and the second approach uses a non-linear model predictive controller for both depth and temperature. Suitable models have been derived and used to design the controllers; a simpler model for the decentralized control and a more extensive, full model used in the non-linear model predictive controller that relates all the important process variables. The two controller designs are compared according to important performance measures, and the achieved increase in performance with the more complex non-linear model predictive controller is evaluated. The non-linear model predictive controller has not been implemented on the real process. Hence, simulations of the closed loop systems using the full model have been used to compare and evaluate the control strategies. The decentralized controller has been implemented on the real system. Two welds have been made using plunge depth control with excellent experimental results, confirming that the decentralized controller design proposed in this thesis can be successfully used. Even though the controller manages to regulate the plunge depth with satisfying performance, simulations indicate that the non-linear model predictive controller achieves even better closed loop performance. This controller manages to compensate for the cross-connections between the process variables, and the resulting closed loop system is almost decoupled. Further research will reveal which control design that will finally be used. / ''Friction stir welding'' har blivit en populär svetsmetod inom många olika tillämpningar. På Svensk Kärnbränslehantering AB (SKB) undersöks möjligheten att använda metoden för att försegla de 5 cm tjocka kopparkapslarna som kommer innehålla det använda kärnbränslet. För att kunna producera repeterbara svetsar utav hög kvalité krävs det att processen regleras. Idag löses detta med en temperaturregulator som reglerar svetszonens temperatur. I detta examensarbete utökas styrsystemet med en regulator för svetsdjupet. Två olika lösningar har utvärderats; först en decentraliserad lösning där temperatur-regulatorn behålls och sedan en lösning med en olinjär modellprediktiv reglering (MPC) som reglerar både djup och temperatur. Passande modeller har tagits fram och har använts för att designa regulatorerna; en enklare modell för den decentraliserade regulatorn och en utökad, komplett modell som används i den olinjära MPC:n och som beskriver alla viktiga variabler i processen. Viktiga prestandamått har jämförts för de båda regulatorstrukturerna och även prestandaökningen med den olinjära MPC:n har utvärderats. Då denna regulator inte har implementerats på den verkliga processen har simuleringar av den kompletta modellen använts för att jämföra och utvärdera regulatorstrukturerna. Den decentraliserade regulatorn har implementerats och testats på processen. Två svetsar har gjorts och de har givit utmärkta resultat, vilket visar att regulatorstrukturen som presenteras i rapporten fungerar bra för reglering av svetsdjupet. Trots att den implementerade regulatorn klarar av att reglera svetsdjupet med godkänt resultat, så visar simuleringar att den olinjära MPC:n ger ännu bättre reglerprestanda. Denna regulator kompenserar för korskopplingar i systemet och resulterar i ett slutet system som är nästan helt frikopplat. Ytterligare forskning kommer avgöra vilken av strategierna som kommer att användas i slutprodukten.

Abstract In this thesis, we use a high power 1550 nm DFB laser and a Ti:LiNbO3 Mach-Zehnder modulator to construct an externally modulated trensmitter for CATV lightwave system. We use two methods to reduce the problem caused by stimulated Brillouin scattering (SBS) effect in externally modulated AM video system by using high-frequency phase modulation and low-frequency dithering techniques. In this experiment, the SBS threshold can be increased by 6 dB. We also design a automatic gain control (AGC) circuit with a 10 dB dynamic range in our transmitter. After addition with a home-made predistortion linearized circuit, the system performance of this transmitter in a 20 km single-mode fiber link carrying 60 NTSC channels can be achieved with a CNR¡Ù46~52 dB¡BCSO¡Ø-68~-73 dBc¡BCTB¡Ø-59~-63 dBc. As the number of channels increased from 60 to 80, we can obtain CNR¡Ù46~51 dB, CSO¡Ø-65.5~-71 dBc, and CTB¡Ø-55~-60.4 dBc. According to preceding description, we know that our trensmitter can carry 60 ~ 80 NTSC channels.

There is a considerable scope for improving the temperature control of exothermic processes. In this thesis, a sub-optimal control strategy is developed through utilizing the dynamic, simulation tool. This scheme is built around easily obtained knowledge of the system and still retains flexibility. It can be applied to both exothermic batch and fed-batch processes. It consists of servo and regulatory modes, where a Generalized Predictive Controller (GPC) was used to provide self-tuning facilities. The methods outlined allow for limited thermal runaway whilst keeping some spare cooling capacity to ensure that operation at constraints are not violated. A special feature of the method proposed is that switching temperatures and temperature profiles can be readily found from plant trials whilst the addition rate profile Is capable of fairly straightforward computation. The work shows that It is unnecessary to demand stability for the whole of the exothermic reaction cycle, permitting a small runaway has resulted in a fast temperature response within the given safety margin. The Idea was employed for an exothermic single Irreversible reaction and also to a set of complex reactions. Both are carried out in a vessel with a heating/cooling coil. Two constraints are Imposed; (1) limited heat transfer area, and (11) a maximum allowable reaction temperature Tmax. The non-minimum phase problem can be considered as one of the difficulties in managing exothermic fed-batch process when cold reactant Is added to vessel at the maximum operating temperature. The control system coped with this within limits, a not unexpected result. In all cases, the new strategy out-performed the conventional controller and produced smoother variations in the manipulated variable. The simulation results showed that batch to batch variations and disturbances In cooling were successfully handled. GPC worked well but can be susceptible to measurement noise.

[Truncated abstract] This thesis is split into two parts. In part one; A 50 K dual mode oscillator, the aim of the project was to build a 50 K precision oscillator with frequency stability on the order of 1014 from 1 to 100 seconds. A dual-mode temperature compensation technique was used that relied on a turning point in the frequency-temperature relationship of the difference frequency between two orthogonal whispering gallery modes in a single sapphire crystal. A cylindrical sapphire loaded copper cavity resonator was designed, modelled and built with a turning point in the difference frequency between an E-mode and H-mode pair at approximately 52.5 K . . . The frequencies and Q-factors of whispering spherical modes in the 3-12 GHz range in the fused silica resonator are measured at 6, 77 and 300 K and the Q-factor is used to determine the loss tangent at these temperatures. The frequency and Q-factor temperature dependence of the TM2,1,2 whispering gallery mode at 5.18 GHZ is used to characterise the loss tangent and relative permittivity of the fused silica from 4-300 K. Below 22 K the frequency-temperature dependence of the resonator was found to be consistent with the combined effects of the thermal properties of the dielectric and the influence of an unknown paramagnetic impurity, with a spin resonance frequency at about 138 ± 31 GHz. Below 8 K the loss tangent exhibited a 9th order power law temperature dependence, which may be explained by Raman scattering of Phonons from the paramagnetic impurity ions. A spherical Bragg reflector resonator made from multiple concentric dielectric layers loaded in a spherical cavity that enables confinement of field in the centre of the resonator is described. A set of simultaneous equations is derived that allow the calculation of the required dimensions and resonance frequency for such a resonator and the solution is confirmed using finite element analysis. A spherical Bragg reflector resonator is constructed using Teflon and free-space as the dielectric materials. A Q-factor of 22,000 at 13.87 GHz was measured and found to compare well with the design values.

Ο στόχος της παρούσας διπλωματικής εργασίας είναι ο έλεγχος και αποκατάσταση της θερμοκρασίας και της υγρασίας από απόσταση σε ένα χώρο ο οποίος απαιτεί συγκεκριμένες τιμές των δύο παραπάνω μεγεθών. Ένας τέτοιος χώρος μπορεί να είναι μια αίθουσα χειρουργείου ή μια μονάδα εντατικής θεραπείας. Ανάλογα με τις επιθυμητές θερμοκρασίες που έχουν τεθεί, ενεργοποιούνται οι βάνες του θερμαντικού ή του ψυκτικού στοιχείου. Όταν η υγρασία του χώρου είναι κατώτερη της επιθυμητής, ενεργοποιείται η τρίοδος βάνα ατμού. Όταν η υγρασία του χώρου είναι υψηλότερη της επιθυμητής ενεργοποιείται η τρίοδος βάνα του ψυκτικού στοιχείου για επιπλέον ψύξη (αφύγρανση) και παράλληλα, αν χρειαστεί ενεργοποιεί και την τρίοδο βάνα του θερμαντικού στοιχείου για να διατηρήσει τη θερμοκρασία του χώρου στα επιθυμητά επίπεδα. Όλα αυτά υλοποιούνται με τη βοήθεια του PLC S7 300 όσο αφορά το λειτουργικό μέρος, της μονάδας CP 343-1 Lean για την επικοινωνία της εγκατάστασης από απόσταση μέσω ethernet, το LabVIEW 9.0 για την υλοποίηση του SCADA(Supervisory Control and Data Acquisition) και τέλος ο OPC SERVER της National instrument για την επικοινωνία του PLC S7 300 με το LabVIEW 9.0. / The scope of this thesis is the control and restoration of temperature and humidity from distance in environments which demand precise values of these two measurements. Such an environment can be an Operating Room or an Intensive Care Unit. The valves of the heating or the cooling element are activated according to the desired temperature. When room humidity is below the desired one, the dew three-port valve is activated. On the other hand when humidity is above the desired level the three-port valve of the cooling element is activated for further cooling (dehydration) and at the same time, if needed, it activates the three-port valve of the heating element to maintain the room temperature at the desired level. This is possible with the use of PLC S7 300, when it comes to the functional part, the CP 343-1 Lean unit for the distant communication of the installation through the use of Ethernet, the LabVIEW 9.0 for the implementation of the SCADA(Supervisory Control and Data Acquisition) and the OPC SERVER of the National Instrument for the communication of the PLC S7 300 with LabVIEW 9.0.