Design Of Linear Quadratic Regulator Controller With Adjustable Gain Function For Rotary Inverted Pendulum System

Design of controllers for non-linear systems has long drawn the attention of researchers especially in the fields of robotics, aerospace engineering and marine engineering. A classic example of a non-linear under-actuated control system is the balance control for a rotary inverted pendulum. Basically, the control approach for such system focusses on torque control of the servo-motor for the purpose of rotating the arm and stabilising the pendulum in its upright position at the shortest possible time. The aim of this research is to supplement and further enhance the control performance of a linear quadratic regulator (LQR) controller with focus on reduced response time and degree of oscillation of the pendulum with added robustness against input disturbance applied to the pendulum position and voltage to the motor. Initially, this thesis comprehensively analysed the LQR controller parameters based on minimal balance time of the pendulum. The LQR controller by itself produced high degree of oscillations, long balance time and poor robustness against input disturbance. As an enhancement over this approach, an adjustable gain was added to the existing LQR control structure. The results showed that for a 30° balancing control, the LQR controller with adjustable gain managed to reduce as much as 70% in the balance time and 98% in the degree of oscillation, while improved its robustness by producing faster balance time and lower oscillation upon excitation by input disturbance forces. In conclusion, the LQR controller with adjustable gain has significantly improved the control performance of the rotary inverted pendulum system

Positioning Control Of Pneumatic Artificial Muscle Systems Using Improved Nominal Characteristic Trajectory Following Control

Pneumatic Artificial Muscle (PAM) is a new type of pneumatic actuator that duplicates the behaviour of skeletal muscle, where it contracts to generate a pulling force via pressurised air and retracts passively when air is depressurised. The PAM has the characteristics that meet the need of robotic applications, such as lightweight, high power-to-weight ratio performance, and safe in use characteristic. However, the PAM exhibits strong nonlinear characteristics which are difficult to be modelled precisely, and these characteristics have led to low controllability and difficult to achieve high precision control performance. This research aims to propose and clarify a practical controller design method for motion control of a pneumatic muscle actuated system. A nominal characteristic trajectory following (NCTF) control is proposed, and this controller emphasises simple design procedure, which it is designed without the exact model parameters, and yet is able to demonstrate high performance in both point-to-point and continuous motions. The NCTF control is composed of a nominal characteristic trajectory (NCT) and a PI compensator. The NCT is the reference motion trajectory of the control system, and the PI compensator makes the mechanism motion follows the constructed NCT. The NCT is constructed on a phase plane using the deceleration motion of the mechanism in open-loop positioning condition. However, the conventional NCTF control does not offer a promising positioning performance with the PAM mechanism, where it exhibits large vibration in the steady-state before the mechanism stopping and tends to reduce the motion accuracy. Therefore, the main goal of this study is to improve the conventional NCTF control for high positioning control of the PAM mechanism. The conventional NCTF control is enhanced by removing the actual velocity feedback to eliminate the vibration problem, added an acceleration feedback compensator to the plant model and a reference rate feedforward to solve the low damping characteristic of the PAM mechanism in order to improve the tracking following characteristic. The design procedure of the improved NCTF control remains easy and straightforward. The effectiveness of the proposed controller is verified experimentally and compared with the conventional NCTF and classical PI controls in positioning and tracking motion performances. The experimental results proved that the improved NCTF control reduced the positioning error up to 90% and 63% as benchmarked to the PI and conventional NCTF controls respectively, while it reduced up to 92% (PI) and 95% (NCTF) in the tracking error. In the robustness evaluation, the comparative experimental results demonstrated that the improved NCTF control has higher robust against the irregular signals than the PI and the conventional NCTF controls. This can be concluded that, the improved NCTF control has demonstrated high positioning accuracy and fast tracking performance at different working range and frequencies as well as high robustness against the irregular signals. Overall, the improved NCTF control has showed the capability in performing high precision motion and offered promising results for the PAM mechanism

Practical Controller Design For Ultra-Precision Positioning Of Stages With A Pneumatic Artificial Muscle Actuator

This paper presents a practical controller design method for ultraprecision positioning of pneumatic artificial muscle actuator stages. Pneumatic artificial muscle (PAM) actuators are safe to use and have numerous advantages which have brought these actuators to wide applications. However, PAM exhibits strong non-linear characteristics, and these limitations lead to low controllability and limit its application. In practice, the non-linear characteristics of PAM mechanism are difficult to be precisely modeled, and time consuming to model them accurately. The purpose of the present study is to clarify a practical controller design method that emphasizes a simple design procedure that does not acquire plants parameters modeling, and yet is able to demonstrate ultraprecision positioning performance for a PAM driven stage. The practical control approach adopts continuous motion nominal characteristic trajectory following (CM NCTF) control as the feedback controller. The constructed PAM driven stage is in low damping characteristic and causes severe residual vibration that deteriorates motion accuracy of the system. Therefore, the idea to increase the damping characteristic by having an acceleration feedback compensation to the plant has been proposed. The effectiveness of the proposed controller was verified experimentally and compared with a classical PI controller in point-topoint motion. The experiment results proved that the CM NCTF controller demonstrates better positioning performance in smaller motion error than the PI controller. Overall, the CM NCTF controller has successfully to reduce motion error to 3µm, which is 88.7% smaller than the PI controlle

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability

Somatic Mutational Landscape of Splicing Factor Genes and Their Functional Consequences across 33 Cancer Types

Hotspot mutations in splicing factor genes have been recently reported at high frequency in hematological malignancies, suggesting the importance of RNA splicing in cancer. We analyzed whole-exome sequencing data across 33 tumor types in The Cancer Genome Atlas (TCGA), and we identified 119 splicing factor genes with significant non-silent mutation patterns, including mutation over-representation, recurrent loss of function (tumor suppressor-like), or hotspot mutation profile (oncogene-like). Furthermore, RNA sequencing analysis revealed altered splicing events associated with selected splicing factor mutations. In addition, we were able to identify common gene pathway profiles associated with the presence of these mutations. Our analysis suggests that somatic alteration of genes involved in the RNA-splicing process is common in cancer and may represent an underappreciated hallmark of tumorigenesis

Characterization Of Pneumatic Artificial Muscle System In An Opposing Pair Configuration

Pneumatic artificial muscle (PAM) is a pneumatic actuator that commonly used in the biomimetic robotic devices in rehabilitation applications due to its advantageous in high power-to-weight ratio and high degree of safety in use characteristics. Several techniques exist in the literature for the PAM system modeling, and these include theoretical modeling, phenomenological modeling and empirical modeling. This paper focuses on explaining the experimental setup of an opposing pair configuration of PAM system, and gives an analysis of the pneumatic muscle system dynamic in the theoretical modeling. The simulated dynamic model is compared with the actual PAM system for the validation in the open-loop step and sinusoidal positioning responses and pressures. It is concluded that the simulation result is verified and agreed with the actual system