Éric Poulin

Development and evaluation of an auto-tuning and adaptive PID controller

Abstract This paper describes the design of a practical auto-tuning and adaptive single-input-single-output (SISO) PID controller (AAC). The AAC can control processes with stable and unstable zeros, processes with an integrator, unstable processes and standard aperiodic processes. It uses an explicit identification with a recursive parameter estimation of a second-order with delay model. The regulator tuning methods are based on an approximate minimization of the ITAE criterion by applying pole-zero cancellation, phase margin and maximum peak resonance specifications, with special considerations for delays, unstable zeros and poles. The data filtering, the identification, the tuning mechanism and the supervisory shell are described. Useful guidelines for PI and PID tuning for SISO processes are given. The AAC performances are compared using a benchmark test with commercial adaptive PID controllers: Foxboro 760C, Fisher DPR 910 and Leeds & Northrup Electromax V.

PI settings for integrating processes based on ultimate cycle information

Presents simple proportional integral (PI) tuning formulas for integrating processes. They are based on the knowledge of the ultimate gain and the ultimate period. This information can be obtained by performing a classical ultimate cycle experiment or by using the relay feedback technique. Refined settings are proposed when the process gain is known. The tuning method is based on a maximum peak resonance specification. The results are compared to those obtained with the Ziegler-Nichols settings. Coherent performances are obtained over a wide range of linear integrating processes.

Fast, automatic, and accurate catheter reconstruction in HDR brachytherapy using an electromagnetic 3D tracking system

PURPOSE In high dose rate brachytherapy (HDR-B), current catheter reconstruction protocols are relatively slow and error prone. The purpose of this technical note is to evaluate the accuracy and the robustness of an electromagnetic (EM) tracking system for automated and real-time catheter reconstruction. METHODS For this preclinical study, a total of ten catheters were inserted in gelatin phantoms with different trajectories. Catheters were reconstructed using a 18G biopsy needle, used as an EM stylet and equipped with a miniaturized sensor, and the second generation Aurora(®) Planar Field Generator from Northern Digital Inc. The Aurora EM system provides position and orientation value with precisions of 0.7 mm and 0.2°, respectively. Phantoms were also scanned using a μCT (GE Healthcare) and Philips Big Bore clinical computed tomography (CT) system with a spatial resolution of 89 μm and 2 mm, respectively. Reconstructions using the EM stylet were compared to μCT and CT. To assess the robustness of the EM reconstruction, five catheters were reconstructed twice and compared. RESULTS Reconstruction time for one catheter was 10 s, leading to a total reconstruction time inferior to 3 min for a typical 17-catheter implant. When compared to the μCT, the mean EM tip identification error was 0.69 ± 0.29 mm while the CT error was 1.08 ± 0.67 mm. The mean 3D distance error was found to be 0.66 ± 0.33 mm and 1.08 ± 0.72 mm for the EM and CT, respectively. EM 3D catheter trajectories were found to be more accurate. A maximum difference of less than 0.6 mm was found between successive EM reconstructions. CONCLUSIONS The EM reconstruction was found to be more accurate and precise than the conventional methods used for catheter reconstruction in HDR-B. This approach can be applied to any type of catheters and applicators.

Receding Horizon Model-Based Predictive Control for Dynamic Target Tracking; a Comparative Study

when the targets are moving. This article describes an application of receding horizon model-based predictive control for UAV target tracking in a dynamic environment. The advantage that predictive control oers over traditional control strategies is that it can account for predicted/future UAV and target trajectories. As such, the proposed method is compared to ve existing target tracking algorithms to demonstrate its eectiveness. For each tracking algorithm, simulations are conducted to test the UAV’s aptitude to track a moving ground target and performance metrics, namely the mean and maximum UAV-to-target distance for the simulation duration, are used to evaluate each method. Simulation results demonstrate that the proposed UAV guidance strategy based on predictive control improves the aircraft’s ability to track a dynamic ground target.

Dynamic data reconciliation in mineral and metallurgical plants

Abstract Data reconciliation is a well-known technique to improve accuracy and reliability of plant measurements. It relies on process models that could range from simple mass and energy conservation equations to complete causal dynamic models. Generally, precise estimates imply detailed plant models that could be difficult to build and update in practice. The trade-off between modeling efforts and estimation performances has thus lead to various approaches to deal with plant dynamics. The objective of the paper is to review and compare most common observers used for dynamic data reconciliation in the mineral and metallurgical processing industries. Comparisons are carried out using a separation unit and a flotation circuit as simulated benchmark plants. Observer performances are evaluated in terms of variance reduction. Strengths and weaknesses of the different methods are highlighted. Aspects such as estimation of model parameters, detection of gross errors, and handling of bilinear equations and plant non-linearities are discussed.

Comparison of dose and catheter optimization algorithms in prostate high-dose-rate brachytherapy

PURPOSE The purpose of this work was to compare the hybrid inverse treatment planning optimization (HIPO), inverse dose-volume histogram-based optimization (DVHO), and fast simulated annealing stochastic algorithm (IPSA). The catheter optimization algorithm HIPO was also compared with the Centroidal Voronoi Tessellation (CVT) algorithm. METHODS AND MATERIALS In this study, eight high-dose-rate prostate cases were randomly selected from an anonymized bank of patients. Oncentra Prostate v4.1 was used to run DVHO and the HIPO catheter optimization (HIPO_cat), whereas Oncentra Brachy v4.3 was used for the remaining. For fixed catheter configurations, DVHO plans were compared with IPSA and HIPO. For catheter positions optimization, CVT and HIPO_cat algorithms were compared with standard clinical template plans. CVT catheters were further restrained to the template grid (CVT_grid) and compared with HIPO_cat. RESULTS For dose optimization, IPSA and HIPO were not different from each other. The urethra D10 and the computation time were found significantly better with IPSA and HIPO compared with DVHO (p < 0.0001). All other dosimetric indices were not statistically different from each others (p > 0.05). For catheter placement, CVT plans were better, whereas HIPO_cat plans were significantly worse (p < 0.05) than standard clinical plans. CVT_grid plans were similar to clinical plans and fulfilling American Brachytherapy Society guidelines down to 12 catheters, whereas HIPO_cat plans do not for all catheter numbers. The CVT algorithm run time was significantly faster than HIPO_cat (p < 0.0001). CONCLUSIONS Dose optimization engines IPSA, DVHO, and HIPO give similar dosimetric results. The CVT approach was found to be better than HIPO_cat and was able to reduce the number of catheters significantly.

Impact of plant dynamics on the performance of steady-state data reconciliation

This paper studies the impact of plant dynamics on the performance of steady-state data reconciliation for processes operating in stationary mode. Data reconciliation can effectively reduce effects of measurement errors on process variables estimation. This has greatly motivated the use of steady-state observers in the process industry. However, processes are operating under unsteady-state conditions and the fundamental hypothesis of steady-state is not respected. The objective of the paper is to develop criteria for assessing the impact of stationary disturbances on estimates quality and therefore to propose applicability indices for steady-state data reconciliation methods in disturbed plants. A generic criterion based on generalized variance is given and criteria are proposed for plant performance indicators using variance reduction in specific state-space directions. The various applicability indices are illustrated through a material balance example for a simulated mineral separation circuit and the steady-state approach is compared to an optimal stationary data reconciliation method.

A procedure for the design and evaluation of decentralised and model-based predictive multivariable controllers for a pellet cooling process

The cooling zone of an induration furnace is a highly interactive multivariable process with strong nonlinearities and dissimilar dynamics. Linear controllers, implemented on a first-principles process model, are unable to properly control the unit in a wide operating range. This paper proposes a design procedure which considers relevant process characteristics, such as nonlinearity, interaction, directionality, and dynamics, for the synthesis of decentralised extended PIDs and model-based predictive controllers (MPCs). Linear controllers with variable transformations are used since the process model shows that a Hammerstein model can approximate the process nonlinear behaviour. The decentralised PIDs are tuned using efficient rules that take into account the process interaction. The performance of both control strategies is evaluated for set-point tracking, disturbance rejection, and robustness to modelling errors. Similar results are obtained for the gas temperature control, which is the most important process variable. Slightly better results are obtained with the MPC for the gas pressure, the fastest dynamic variable.

Control of a Hovering Mini Fixed Wing Aerial Vehicle

This paper describes an approach for designing a stabilizing control strategy of a mini fixed wing aerial vehicle in hovering mode. This flight mode gives the ability to navigate inside a constrained environment. An inertial measurement unit is used to measure the attitude. The increased mass due to the on-board sensor poses a greater challenge to developing a functional autonomous vehicle than previous studies that employed o-board sensors for attitude sensing. Linear transfer functions are proposed for attitude with slow transits modeling. The design is achieved with a frequency domain method involving the Nichols chart. The control of a hovering vehicle requires ecient tuning methods capable of insuring robustness to account for model errors. Simulation and flight test results are presented to show the performance obtained with the proposed tuning method.

Fully thoracoscopic pulmonary lobectomy and specimen extraction through rib segment resection : Preliminary report

AbstractBackground: A technique of fully thoracoscopic pulmonary lobectomy with rib-segment resection for specimen extraction is described, and preliminary results in 18 patients are presented. Methods: Surgery is performed through four 15-mm ports. For all lobes except one, the surgeon operates in front of the patient, where the rib spaces are widest and rib-space trauma is less. When lobar dissection is complete, specimen extraction is performed after resection of a rib segment proportional to tumor size. Muscle section is kept to a minimum. There is no rib retraction. Results: There were no deaths, three conversions to open surgery, and three major complications. Average postoperative stay was 5.4 days for patients without complications and 9.6 days for patients with complications. In total six patients presented with some degree of air leaks, and two had post-thoracotomy pain (>2 months duration). The literature is reviewed to analyze current techniques and to define parameters of a truly minimally invasive pulmonary lobectomy. Conclusions: This technique is safe and promising; however, thoracoscopic lobectomy still needs refining. Before valid randomized studies comparing thoracoscopic lobectomy and muscle-sparing thoracotomy or posterolateral thoracotomy can be credible, technical issues related to the production of a truly minimally invasive procedure should be resolved.