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284 results on '"Walker, I.D."'

2. Fault identification for robot manipulators

Author

McIntyre, M.L., Dixon, W.E., Dawson, D.M., and Walker, I.D.

Subjects
Robot, Robotics -- Research, Robots -- Research
Abstract

Several factors must be considered for robotic task execution in the presence of a fault, including: detection, identification, and accommodation for the fault. In this paper, a nonlinear observer is used to identify a class of actuator faults once the fault has been detected by some other method. Advantages of the proposed fault-identification method are that it is based on the nonlinear dynamic model of a robot manipulator (and hence, can be extended to a number of general Euler Lagrange systems), it does not require acceleration measurements, and it is independent from the controller. A Lyapunov-based analysis is provided to prove that the developed fault observer converges to the actual fault. Experimental results are provided to illustrate the performance of the identification method. Index Terms--Fault identification, nonlinear dynamics, robot manipulator.

Published
2005

4. Clotting and chromogenic factor VIII assay variability in post-infusion and spiked samples containing full-length recombinant FVIII or recombinant factor VIII Fc fusion protein (rFVIIIFc)

Author

Kitchen, S., Jennings, I., Makris, M., Kitchen, D.P., Woods, T.A.L., and Walker, I.D.

Subjects
congenital, hereditary, and neonatal diseases and abnormalities, hemic and lymphatic diseases
Abstract

INTRODUCTION: Variability in FVIII measurement is a recognized problem. There are limited data for samples containing recombinant Factor VIII Fc fusion protein (rFVIIIFc). Many studies use samples for which factor concentrate has been spiked into FVIII deficient plasma in vitro. This approach requires validation. AIM/METHODS: Four samples were distributed in a UK National External Quality Assessment Scheme for Blood Coagulation (NEQAS BC) survey. One contained Advate (full-length recombinant FVIII) (rFVIII) added to FVIII deficient plasma, one was from a severe haemophilia A patient after infusion of Advate, one was prepared by addition of rFVIIIFc (marketed as Elocta/Eloctate) to FVIII deficient plasma and the fourth was collected from a severe haemophilia A patient following rFVIIIFc (Eloctate) infusion. Fifty-three haemophilia centres (UK and Scandinavia) performed one-stage FVIII assays and 27 performed chromogenic FVIII assays. RESULTS/CONCLUSIONS: One-stage assays gave significantly lower results than chromogenic assays by 7% (P

Published
2019

6. Increased fetal loss in women with heritable thrombophilia

Author

Preston, F.E., Rosendaal, F.R., Walker, I.D., Briet, E., Berntorp, E., Conard, J., Fontcuberta, J., Makris, M., Mariani, G., Noteboom, W., Pabinger, I., Legnani, C., Scharrer, I., Schulman, S., and Meer, F.J.M. van der

Subjects
Thrombosis -- Health aspects, Fetal death -- Risk factors, Still-birth -- Risk factors, Protein C deficiency -- Health aspects, Protein S deficiency -- Health aspects, Pregnancy, Complications of -- Physiological aspects
Published
1996

8. Robustness issues for kinematically redundant manipulator control

Author

Nguyen, L.A., Walker, I.D., and DeFigueiredo, R.J.P.

Subjects
Manipulators -- Models, Robots -- Control systems, Kinematics -- Analysis
Abstract

Kinematic redundancy of robotic manipulators has been known to be useful in accomplishing additional performance on top of the main task of tracking desired end effector trajectories. Robustness has been a major concern in manipulator control where exact physical properties of manipulators are unobtainable. In this paper, we review a method of analyzing robustness of joint space controllers for manipulators, and extend the analysis to end effector space control for the first time. We then generalize the approach to the case of kinematically redundant manipulators by introducing the redundancy as part of the manipulator states, and show that kinematic redundancy is useful in making manipulator controllers more robust. The final result of this paper is an optimization problem whose solution determines the self-motion which optimizes the system robustness.

Published
1995

9. Expert system framework for fault detection and fault tolerance in robotics

Author

Visinsky, M.L., Cavallaro, J.R., and Walker, I.D.

Subjects
Expert systems -- Design and construction, Robotics -- Research, Fault location (Engineering) -- Methods, Computers, Electronics, Engineering and manufacturing industries
Abstract

Fault tolerance is of increasing importance for modern robots. The ability to detect and tolerate failures enables robots to effectively cope with internal failures and continue performing assigned tasks without the need for immediate human intervention. To monitor fault tolerance actions performed by lower level routines and to provide higher level information about a robot's recovery capabilities, we present an expert system and critic which together form a novel and intelligent fault tolerance framework integrating fault detection and tolerance routines with dynamic fault tree analysis. A higher level, operating system inspired critic layer provides a buffer between robot fault tolerant operations and the user. The expert system gives the framework the modularity and flexibility to quickly convert between a variety of robot structures and tasks. It also provides a standard interface to the fault detection and tolerance software and a more intelligent means of monitoring the progress of failure and recovery throughout the robot system. The expert system further allows for prioritization of tasks so that recovery can take precedence over less pressing goals. Fault trees are used as a standard database to reveal the components essential to fault detection and tolerance within a system and detail the interconnection between failures in the system. The trees are also used quantitatively to provide a dynamic estimate of the probability of failure of the entire system or various subsystems.

Published
1994

15. Factor VIII assay variability in postinfusion samples containing full length and B-domain deleted FVIII

Author

Kitchen, S., Jennings, I., Makris, M., Kitchen, D.P., Woods, T.A.L., and Walker, I.D.

Abstract

Introduction\ud \ud Although the variability in factor VIII (FVIII):C measurement is well recognized, this has not been widely reported for post-FVIII infusion samples.\ud Aim/Methods\ud \ud Three samples from haemophilia A patients were distributed in a UK National External Quality Assessment Scheme survey, each after treatment with either ReFacto AF, Kogenate FS or Advate. Fifty-two UK haemophilia centres performed FVIII assays using one-stage (n = 46) and chromogenic (n = 10) assays. Centres calibrated assays with the local plasma standard and with ReFacto AF laboratory standard for the ReFacto AF sample.\ud Results/Conclusions\ud \ud Chromogenic assays gave significantly higher results than one-stage assays (P < 0.0001, 32% difference) in the post-Kogenate sample but not in the post-ReFacto AF (11% higher by chromogenic assay, ns) or post-Advate samples (3% lower by chromogenic, ns) when assays were calibrated with plasma standards. Twenty centres used all Instrumentation Laboratory (IL)-activated partial thromboplastin time reagents (Synthasil)/IL deficient plasma/reference plasma) in the one-stage assay and 15 used all Siemens reagents (Actin FS/Siemens deficient plasma/reference plasma); this made a significant difference to results post-ReFacto AF (41% higher by IL reagents, P < 0.0001) and Advate (39% higher by IL reagents, P < 0.0001), but not Kogenate (7% higher by IL, ns) when calibrated with plasma standards. Differences between results obtained with different one-stage assay reagents for monitoring Advate have implications for dosing patients. Furthermore, there was considerable inter-laboratory variation as indicated by CVs in the range 15–26% for chromogenic assay and 12–19% for one-stage assay results. This study suggests that external quality assessment schemes should offer participation in post-FVIII infusion schemes where haemophilic patients are monitored.

Published
2016

19. Combined prednisolone and intravenous immunoglobulin treatment for acquired factor VIII inhibitors: a 2-year review

Author

Dykes, A.C., Walker, I.D., Lowe, G.D.O., and Tait, R.C.

Subjects
RM, hemic and lymphatic diseases, QP, RC
Abstract

Acquired inhibitors to factor VIII (FVIII) are rare, but life- threatening in up to 22% of cases. The optimal therapy for suppression of these inhibitors remains unclear. Prednisolone is the mainstay of therapy, producing responses in approximately 30% of cases. Intravenous immunoglobulin (IVIg) has a similar response rate, but a more rapid effect. We report the results of prednisolone 1 mg kg(-1) combined with IVIg 2 g kg(-1) in divided doses as first-line therapy in seven consecutive patients with acquired FVIII inhibitors. All patients were bleeding at the time of diagnosis with prolonged activated partial thromboplastin time. There were four complete responses, one partial response, one nonresponse and one with an inadequate follow-up for assessment of response, giving an overall response rate of 71%. In all complete responders the inhibitor declined rapidly and was undetectable by day 21 from start of treatment. Therapy was well tolerated and responses have been maintained off treatment for 2-8 months. This is a safe, well-tolerated rapidly acting regimen with good response rates.

Published
2001

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