A Fast On-Line Estimator of the Two Main Vibration Modes of Flexible Structures From Biased and Noisy Measurements

Vibrations are present in many mechanical structures and machines, and are often associated with their elastic parts. Characterizing these vibrations, i.e., obtaining their frequencies, amplitudes and phases, is of most interest in many applications ranging from the maintenance of civil structures to motion control. This article presents a method for the on-line and reliable identification of the defining parameters of two unknown sinusoidal signals through the use of their measured sum in the presence of noise and an offset. It is based on the algebraic derivative approach, defined in the frequency domain, which yields exact calculation formulae for the unknown parameters of the signal, i.e., the amplitudes, phases and frequencies of the two sinusoids and the value of the constant term. The on-line estimation is performed in a time interval which is only a fraction of the first full cycle of the slower component of the measured signal. This feature allows the algorithm to be used to monitor time varying parameters in these vibration signals. This algorithm has been used in experiments with a flexible beam, which is a representative platform of a vibrating mechatronic system. It estimated all the vibration signal parameters quickly and accurately, proved to be insensitive to high frequency noises, and accurately tracked the time variations of the signal parameters

Passivity-Based Control Improvement of Single-Link Flexible Manipulators by a Two-Degree-of-Freedom PID Motor controller

A new approach to a previous passivity-based control scheme of single-link flexible manipulators is presented herein. Such previous scheme achieves precise positioning of the link tip by combining a position angular control of the motor (inner loop) with a link vibration damping (outer loop), which can be designed independently by decoupling joint and link dynamics with a linear strain feedback. Although, precise positioning can be achieved under large tip payload changes, the used inner loop cannot eliminate the steady-state position error due to the nonlinearities present in the motor. The contribution presented in this work consists of using a two-degree of freedom PID motor controller to solve this problem, eliminating thus the steady-state error while also improving the settling time of the angular position. Simulation and experimental results are carried out to illustrate these improvements

Two-Degrees-of-Freedom Controller delivering zero-error tracking of ramp-like trajectories for nanopositioning systems

Piezoelectrically actuated nanopositioning systems (tube or platform type) are widely employed in applications where fine mechanical displacements with resolution down to atomic scale are required. This paper presents the design, analysis, and validation of a new control scheme based on the structure of the traditional Two-Degrees-of-Freedom (2DOF) PID controller. The proposed controller is established based on a linear continuous input-output nominal model, and presents a simple structure composed by two second order transfer functions. Despite its simplicity, the controller studied in this paper is able to achieve zero error in the tracking of ramp input signals and, therefore, in the slopes of triangular signals, typically used in nanopositioning applications to trace a raster pattern. The controller also suppresses the unmodeled nonlinearities of the piezoelectric actuated nanopositioning systems without the need of an hysteresis model or a state observer. Moreover, the stability of the control system is proved, and its effectiveness is validated through experimental chattering-free control on a piezoelectric stack-actuated nanopositioning platform. Results demonstrate that the proposed controller is superior to the conventional polynomial-based, proportional-integral, and resonant controllers proposed in literature for motion-tracking tasks in nanopositioning systems

A Two-Stage Control Scheme of Single-Link Flexible Manipulators

A new control scheme composed of two independent stages utilised to achieve precise positioning of single-link flexible manipulators is presented herein. Traditional techniques for the control of single-link flexible manipulators utilise only one actuator and two types of sensor measurement (e.g the angular position of the motor and acceleration or strain measurements) to move the manipulator and in order to damp the residual vibrations produced in the displacement of the manipulator. However, in the proposed control scheme another additionally pair actuator-sensor is utilised to improve the speed and precision of the controlled system. On the one hand a motor and the readings of a rotary encoder are utilised in a first stage to displace the manipulator, using the strain measurements in order to damp the high amplitude and low frequency residual vibrations. On the other hand piezoelectric actuators are utilised in conjunction with displacement measures of the tip of the manipulator in order to damp the low amplitude and high frequency residual vibrations which deteriorate the accuracy of the positioning achieved by the traditional control techniques. Simulation and experimental results are carried out to illustrate these improvements

Fractional-order integral resonant control of collocated smart structures

This paper proposes a fractional-order integral controller, FI, which is a simple, robust and well-performing technique for vibration control in smart structures with collocated sensors and actuators. This new methodology is compared with the most relevant controllers for smart structures. We demonstrate that the proposed controller improves the robustness of the closed-loop system to changes in the mass of the payload at the tip. The previous controllers are robust in the sense of being insensitive to spillover and maintaining the closed-loop stability when changes occur in the plant parameters. However, the phase margin of such closed-loop systems (and, therefore, their damping) may change significantly as a result of these parameter variations. In this paper we explore the possibility of increasing the phase margin robustness by using a fractional-order controller with a very simple structure. We have applied this controller to an experimental smart structure, and simulations and experiments have shown the improvement attained with this new technique in the removal of the vibration in the structure when the mass of the payload at the tip change

Patients with Crohn's disease have longer post-operative in-hospital stay than patients with colon cancer but no difference in complications' rate

BACKGROUNDRight hemicolectomy or ileocecal resection are used to treat benign conditions like Crohn's disease (CD) and malignant ones like colon cancer (CC).AIMTo investigate differences in pre- and peri-operative factors and their impact on post-operative outcome in patients with CC and CD.METHODSThis is a sub-group analysis of the European Society of Coloproctology's prospective, multi-centre snapshot audit. Adult patients with CC and CD undergoing right hemicolectomy or ileocecal resection were included. Primary outcome measure was 30-d post-operative complications. Secondary outcome measures were post-operative length of stay (LOS) at and readmission.RESULTSThree hundred and seventy-five patients with CD and 2,515 patients with CC were included. Patients with CD were younger (median = 37 years for CD and 71 years for CC (P < 0.01), had lower American Society of Anesthesiology score (ASA) grade (P < 0.01) and less comorbidity (P < 0.01), but were more likely to be current smokers (P < 0.01). Patients with CD were more frequently operated on by colorectal surgeons (P < 0.01) and frequently underwent ileocecal resection (P < 0.01) with higher rate of de-functioning/primary stoma construction (P < 0.01). Thirty-day post-operative mortality occurred exclusively in the CC group (66/2515, 2.3%). In multivariate analyses, the risk of post-operative complications was similar in the two groups (OR 0.80, 95%CI: 0.54-1.17; P = 0.25). Patients with CD had a significantly longer LOS (Geometric mean 0.87, 95%CI: 0.79-0.95; P < 0.01). There was no difference in re-admission rates. The audit did not collect data on post-operative enhanced recovery protocols that are implemented in the different participating centers.CONCLUSIONPatients with CD were younger, with lower ASA grade, less comorbidity, operated on by experienced surgeons and underwent less radical resection but had a longer LOS than patients with CC although complication's rate was not different between the two groups

The impact of stapling technique and surgeon specialism on anastomotic failure after right?sided colorectal resection: an international multicentre, prospective audit

Aim There is little evidence to support choice of technique and configuration for stapled anastomoses after right hemicolectomy and ileocaecal resection. This study aimed to determine the relationship between stapling technique and anastomotic failure. Method Any unit performing gastrointestinal surgery was invited to contribute data on consecutive adult patients undergoing right hemicolectomy or ileocolic resection to this prospective, observational, international, multicentre study. Patients undergoing stapled, side?to?side ileocolic anastomoses were identified and multilevel, multivariable logistic regression analyses were performed to explore factors associated with anastomotic leak. Results One thousand three hundred and forty?seven patients were included from 200 centres in 32 countries. The overall anastomotic leak rate was 8.3%. Upon multivariate analysis there was no difference in leak rate with use of a cutting stapler for apical closure compared with a noncutting stapler (8.4% vs 8.0%, OR 0.91, 95% CI 0.54–1.53, P = 0.72). Oversewing of the apical staple line, whether in the cutting group (7.9% vs 9.7%, OR 0.87, 95% CI 0.52–1.46, P = 0.60) or noncutting group (8.9% vs 5.7%, OR 1.40, 95% CI 0.46–4.23, P = 0.55) also conferred no benefit in terms of reducing leak rates. Surgeons reporting to be general surgeons had a significantly higher leak rate than those reporting to be colorectal surgeons (12.1% vs 7.3%, OR 1.65, 95% CI 1.04–2.64, P = 0.04). Conclusion This study did not identify any difference in anastomotic leak rates according to the type of stapling device used to close the apical aspect. In addition, oversewing of the anastomotic staple lines appears to confer no benefit in terms of reducing leak rates. Although general surgeons operated on patients with more high?risk characteristics than colorectal surgeons, a higher leak rate for general surgeons which remained after risk adjustment needs further exploration

Relationship between method of anastomosis and anastomotic failure after right hemicolectomy and ileo-caecal resection: an international snapshot audit

Aim: The anastomosis technique used following right-sided colonic resection is widely variable and may affect patient outcome. This study aimed to assess the association between leak and anastomosis technique (stapled vs handsewn). Method: This was a prospective, multicentre, international audit including patients undergoing elective or emergency right hemicolectomy or ileo-caecal resection operations over a 2-month period in early 2015. The primary outcome measure was the presence of anastomotic leak within 30\ua0days of surgery, determined using a prespecified definition. Mixed effects logistic regression models were used to assess the association between leak and anastomosis method, adjusting for patient, disease and operative cofactors, with centre included as a random-effect variable. Results: This study included 3208 patients, of whom 78.4% (n\ua0=\ua02515) underwent surgery for malignancy and 11.7% (n\ua0=\ua0375) underwent surgery for Crohn's disease. An anastomosis was performed in 94.8% (n\ua0=\ua03041) of patients, which was handsewn in 38.9% (n\ua0=\ua01183) and stapled in 61.1% (n\ua0=\ua01858). Patients undergoing handsewn anastomosis were more likely to be emergency admissions (20.5% handsewn vs 12.9% stapled) and to undergo open surgery (54.7% handsewn vs 36.6% stapled). The overall anastomotic leak rate was 8.1% (245/3041), which was similar following handsewn (7.4%) and stapled (8.5%) techniques (P\ua0=\ua00.3). After adjustment for cofactors, the odds of a leak were higher for stapled anastomosis (adjusted OR\ua0=\ua01.43; 95% CI: 1.04\u20131.95; P\ua0=\ua00.03). Conclusion: Despite being used in lower-risk patients, stapled anastomosis was associated with an increased anastomotic leak rate in this observational study. Further research is needed to define patient groups in whom a stapled anastomosis is safe

Predictors for anastomotic leak, postoperative complications, and mortality after right colectomy for cancer: Results from an international snapshot audit

Background: A right hemicolectomy is among the most commonly performed operations for colon cancer, but modern high-quality, multination data addressing the morbidity and mortality rates are lacking. Objective: This study reports the morbidity and mortality rates for right-sided colon cancer and identifies predictors for unfavorable short-term outcome after right hemicolectomy. Design: This was a snapshot observational prospective study. Setting: The study was conducted as a multicenter international study. Patients: The 2015 European Society of Coloproctology snapshot study was a prospective multicenter international series that included all patients undergoing elective or emergency right hemicolectomy or ileocecal resection over a 2-month period in early 2015. This is a subanalysis of the colon cancer cohort of patients. Main Outcome Measures: Predictors for anastomotic leak and 30-day postoperative morbidity and mortality were assessed using multivariable mixed-effect logistic regression models after variables selection with the Lasso method. Results: Of the 2515 included patients, an anastomosis was performed in 97.2% (n = 2444), handsewn in 38.5% (n = 940) and stapled in 61.5% (n = 1504) cases. The overall anastomotic leak rate was 7.4% (180/2444), 30-day morbidity was 38.0% (n = 956), and mortality was 2.6% (n = 66). Patients with anastomotic leak had a significantly increased mortality rate (10.6% vs 1.6% no-leak patients; p 65 0.001). At multivariable analysis the following variables were associated with anastomotic leak: longer duration of surgery (OR = 1.007 per min; p = 0.0037), open approach (OR = 1.9; p = 0.0037), and stapled anastomosis (OR = 1.5; p = 0.041). Limitations: This is an observational study, and therefore selection bias could be present. For this reason, a multivariable logistic regression model was performed, trying to correct possible confounding factors. Conclusions: Anastomotic leak after oncologic right hemicolectomy is a frequent complication, and it is associated with increased mortality. The key contributing surgical factors for anastomotic leak were anastomotic technique, surgical approach, and duration of surgery