52 research outputs found
Dissociated jerk-limited trajectory applied to time-varying vibration reduction
No full textJerk-limited trajectories are a widespread solution for the trajectory planning of industrial machines Tools or robots. It is known that jerk limitation can reduce vibrations and in some cases can totally suppress residual vibration induced by a lightly damped stationary mode. However, for systems with time-varying mode, which is classically the case for configuration dependent mode or load mass variations, the previous result vanishes. This paper proposes to extend the jerk-limited profile (JL) properties to time-varying vibration problem. First, a guideline for designing a dissociated jerk-limited profile (DJL) based on simple and pragmatic Finite Impulse Response (FIR) filtering methodology is presented. Following the guideline, the time-varying vibration reduction principle is detailed. Then, experiments conducted on an industrial 3-axes Cartesian manipulator are presented. The experimental results show that the residual vibration magnitude is reduced to less than 23% of the original level obtained with JL profile and the settling time is reduced by 10%, demonstrating the efficiency of the proposed DJL trajectory planning
Feedrate planning for machining with industrial six-axis robots
No full textThe authors want to thank Stäubli for providing the necessary information of the controller, Dynalog for its contribution to the experimental validations and X. Helle for its material contributions.Nowadays, the adaptation of industrial robots to carry out high-speed machining operations is strongly required by the manufacturing industry. This new technology machining process demands the improvement of the overall performances of robots to achieve an accuracy level close to that realized by machine-tools. This paper presents a method of trajectory planning adapted for continuous machining by robot. The methodology used is based on a parametric interpolation of the geometry in the operational space. FIR filters properties are exploited to generate the tool feedrate with limited jerk. This planning method is validated experimentally on an industrial robot
Improving the Accuracy of Industrial Robots by offline Compensation of Joints Errors
No full textThe use of industrial robots in many fields of industry like prototyping, pre-machining and end milling is limited because of their poor accuracy. Robot joints are mainly responsible for this poor accuracy. The flexibility of robots joints and the kinematic errors in the transmission systems produce a significant error of position in the level of the end-effector. This paper presents these two types of joint errors. Identification methods are presented with experimental validation on a 6 axes industrial robot, STAUBLI RX 170 BH. An offline correction method used to improve the accuracy of this robot is validated experimentally
New Damped-Jerk trajectory for vibration reduction
No full textThis paper derives a jerk-shaped profile to address the vibration reduction of underdamped flexible dynamics of motion system. The jerk-limited profile is a widespread smooth command pattern used by modern motion systems. The ability of the jerk-limited profile to cancel the residual vibration of an undamped flexible mode is clearly explained using an equivalent continuous filter representation and the input shaping formalism. This motivates the design of a new jerk-shaped profile, named Damped-Jerk profile, to extend the previous result to the more common case of underdamped systems. Both simulations and experimental results demonstrate the effectiveness of the proposed Damped-Jerk profile to reduce damped vibration
A Pragmatic Approach to Exploiting Full Force Capacity for Serial Redundant Manipulators
No full textConsidering a set of robotic tasks which involve physical interaction with the environment, the theoretical knowledge of the full force capacity of the manipulator is a key factor in the design or development of an efficient and economically attractive solution. Carrying its own weight while countering forces may be too much for a robot in certain configurations. Kinematic redundancy with regard to a task allows a robot to perform it in a continuous space of articular configurations; space in which the payload of the robot may vary dramatically. It may be impossible to withstand a physical interaction in some configurations, while it may be easily sustainable in others that bring the end-effector to the same location. This becomes obviously more prevalent for a limited payload robot. This letter describes a framework for these kind of operations, in which kinematic redundancy is used to explore the full extent of a force capacity for a givenmanipulator and task (in this letter, the terms “force” and “wrench” may interchangeably refer to two-, three-, or six-dimensional forces depending on the dimension of the problem and on whether they may or may not include components of translational forces and/or moments. Their dimensional definition will be explicitly given whenever specifically needed). A pragmatic force capacity index (FCI) is proposed. The FCI offers a sound basis for redundancy resolution via optimization or complete redundancy exploration, and may provide good hints for end-effector design. A practical use case involving 7-DOFs KUKA LBR iiwa was used to demonstrate the relevance of the proposed method
Comparison and correlation of ki67 expression and gleason score in prediction of biological behaviour of prostatic adenocarcinoma in Tanzanian patients
No full textBackground
Prostate cancer is the second most commonly diagnosed and sixth most lethal cancer in men worldwide, affecting Blacks more than Whites and Asians, with geographical variations. Not all men diagnosed with prostate cancer will develop a progressive disease; some cancers remain indolent and usually need active surveillance, while others are aggressive thus needing treatment. Gleason score is the most recognized of progression-associated prognosticators, but it misses some cases. Development of prostate cancer progression marker is anxiously awaited, to detect prostate cancer progressive cases missed by Gleason score system. Proliferation markers have been shown to be involved in progression of some human tumours. Ki67 expression contribution in predicting prostate cancer biological behaviour needs to be determined, for use in a combination to Gleason score to offer better prognosis information.
Aim
To compare and correlate Gleason score with Ki67 expression in predicting the biological behaviour of prostatic adenocarcinoma in Tanzanian patients, in regards to prostatic-specific antigen (PSA), stage, progression of the disease and survival duration.
Methods
256 cases of prostatic adenocarcinoma diagnosed at Muhimbili National Hospital (MNH) from January 2005 to December 2006 were retrieved; 214 were retained in the study. The types of specimens were 188 (87.9%) core biopsies, 24 (11.2%) transurethral resection of prostate (TURP) and 2 cases (0.9%) of bone biopsies. A retrospective follow-up of 48 patients was done over 60 months using patients’ files; 42 excluded cases consisted of 29 cases missing tissue blocks and 13 cases without clinical data. Sections of archival tissue blocks were stained with Haematoxylin and Eosin (H&E) and MIB-1 to respectively determine Gleason score and Ki67 index by determining percent of positive cells among at least 500 cells in hotspots. Gleason score was correlated and compared to Ki67 index in terms of PSA, stage, disease progression and patient’s survival among others. Data entry and analysis were done through computer software; P value and 95% confidence interval (CI) were used as measure of variable association.
Results
Prostatic cancer was diagnosed in 34.73% (256/737) of prostate specimens; all cases were acinar adenocarcinoma. Mean age was 70.5 years, with the range of 42 to 96 years. Clinical data suffered poor documentation. Pre-treatment PSA levels were high, mean was 79.578 (2.32 to 500.00) ng/mL. 68.0% had advanced clinical disease, 26.1% had distant metastases. High grades predominated (Gleason score 8-10 in 34.6%, Gleason score 7 in 38.3% of cases). Median Ki67 index in prostatic adenocarcinoma was 10.39% (range 0.0% to 50.94%). 48 cases were followed up along 0.56 to 60 months (mean was 31.2 months); 2 of 15 patients were alive at last follow-up. The mean survival of fully followed-up cases was 24.50 months (95% CI=13.09 to 35.91 months). Gleason score correlated with age (P= 0.000, 95% CI=70.705 to 71.676 years), pre-treatment serum PSA level (P=0.001; 95% CI=75.45 to 84 ng/mL), average tumour extent in tissue (P= 0.000; 95% CI=66.26 to 69.49%), tumour stage (P=0.009), survival duration (P=0.029) and patient’s outcome (P=0.011). Ki67 index decreased with age (P=0.006), increased with Gleason score (P=0.001) and average tumour extent (P=0.032), correlated with disease progression (P=0.020; 95% CI= 1.163 to 6.885) and survival duration (P=0.21). Pre-treatment PSA level significantly correlated with Gleason score but not with Ki67 index; Gleason score rather than Ki67 index predicted tumour stage; both Gleason score and Ki67 index similarly predicted survival duration, but Ki67 index depicted progressive cancer disease cases missed by Gleason score system.
Conclusion
A combination of Gleason score and Ki67 index offers better prognostic information than either alone. The challenge to Ki67 index use is its cost and time consumption. A multicentre prospective study is recommended to confirm these findings. Standard documentation and preventive education on prostate cancer should be implemented and monitored in Tanzania
Modélisation énergétique des éléments de transitique pour une optimisation du pilotage des entrepôts logistiques
No full textCette étude présente l'élaboration d'un simulateur dédié à l'évaluation de la consommation énergétique des composants de transitique d'un entrepôt logistique (navette et élévateur). Ce simulateur intègre les paramètres physiques ainsi que les lois cinématiques de pilotage comme variables d'entrée. Les résultats obtenus démontrent que chaque mouvement de l'élévateur offre une opportunité de récupération partielle d'énergie. L'étude souligne l'intérêt d'approfondir l'examen des dispositifs de stockage et de redistribution de cette énergie récupérée. Une identification plus fine des frottements mécaniques améliorerait significativement la justesse du modèle en matière de consommation et de récupération d'énergie. La combinaison des modèles proposés, associée à une simulation de flux reposant sur un carnet de commande et une configuration d'entrepôt définis, permet d'anticiper précisément la consommation énergétique globale de l'entrepôt. Le recours à ce simulateur facilite l'analyse de l'influence des stratégies de pilotage sur la consommation, et pourrait fonder l'élaboration de nouvelles lois de gestion intégrant le critère énergétique.</div
Prise en compte des phénomènes vibratoires dans la génération de commande des machines-outils à dynamique élevée
No full textLa recherche de performances toujours plus élevées conduit les systèmes de positionnement à dynamique élevée à la limite de leurs possibilités technologiques et structurelles, invalidant de ce fait l'hypothèse classiquement retenue d'une dynamique d'ensemble assimilable à celle d'un corps rigide. Il s'ensuit que la commande du système ne peut plus sous-estimer l'influence des phénomènes vibratoires sur la qualité du suivi de profil, mais doit moduler les efforts moteurs afin de réaliser l'adéquation entre les caractéristiques intrinse ques au système et les critères de rapidité et de précision escomptés. Les travaux développés dans cette étude visent une amélioration du comportement dynamique du système par une action sur la génération de commande. La génération de commande s'articule autour de deux principales fonctions : (1) l'élaboration d'une loi de mouvement pour la ou les variables du système à contrôler servant de référence pour les asservissements (commande indirecte); (2) la définition d'une précommande transformant la loi de mouvement en un signal de référence pour l'entrée du système physique (commande directe). Ces deux fonctions, correctement gérées, permettent de découpler les problèmes de régulation et de suivi de profil. Dans un premier temps, elles sont traitées spécifiquement pour le cas du mouvement d'un système monoaxe. Ainsi, l'influence de différentes classes de lois de mouvement (harmoniques, polynomiales, polynomiales par morceaux ou bang-bang) sur les vibrations et la durée du mouvement est formalisée. Une méthodologie d'élaboration d'une précommande adaptée aux souplesses d'un axe est présentée; elle permet de mettre en exergue les contrainte.The increasing demands in terms of productivity lead the high-dynamics systems to the maximum of their technological and structural capacities, invalidating the classical assumption of a rigid body dynamics. Consequently, the system control cannot neglect the influence of the vibratory phenomena on the accuracy of the contour tracking, but it has to modulate the command efforts in order to realize the adequacy between the intrinsic system characteristics and the speed and accuracy criteria. This study aims at improving the dynamic behavior of these machines by a direct action on the command generation. The command generation is divided into two main functions: (1) the elaboration of a movement law for the system states to control, which is used as reference for controls (indirect control); (2) the definition of a prefilter transforming the movement law into a reference signal for the input of the physical system (direct control). If correctly managed, these two functions make it possible to dissociate the regulation and the contour tracking problems. Initially, they are specifically study in the case of one axis movement. Thus, the influence of various movement laws (harmonic, polynomial, piecewise polynomial or multi-switch bang-bang law) on the vibrations and on the movement time is formalized. A design methodology for the prefilter adapted to the flexibilities of an axis is presented; it puts forward the required degree of continuity, which the law of movement must satisfy. Then, after experimental validations on several high-dynamics test-setups, the results and methodologies are adapted to the contour-tracking problem for two Cartesian axes.PARIS-Arts et Métiers (751132303) / SudocLILLE-Arts et Métiers (593502311) / SudocSudocFranceF
Reducing the Computational Complexity of Mass-Matrix Calculation for High DOF Robots
No full textIncreasingly, robots have more degrees of freedom (DOF), imposing a need for calculating more complex dynamics. As a result, better efficiency in carrying out dynamics computations is becoming more important. In this study, an efficient method for computing the joint space inertia matrix (JSIM) for high DOF serially linked robots is addressed. We call this method the Geometric Dynamics Algorithm for High number of robot Joints (GDAHJ). GDAHJ is non-symbolic, preserve simple formulation, and it is convenient for numerical implementation. This is achieved by simplifying the way to recursively derive the mass-matrix exploiting the unique property of each column of the JSIM and minimizing the number of operations with O(n2) complexity. Results compare favorably with existing methods, achieving better performance over state-of-the-art by Featherstone when applied for robots with more than 13 DOF
A Modified DLS Scheme With Controlled Cyclic Solution for Inverse Kinematics in Redundant Robots
No full textRedundancy in robotic manipulators has many advantages. It is successfully used to achieve better dexterity, and to avoid obstacles, singularities, or the kinematic limitations. However, redundancy makes the inverse kinematics (IK) problem harder to solve. The damped least squares (DLS) is a powerful method for calculating the IK of redundant robots, but it suffers from noncyclicity issue, where a closed curve motion in the Cartesian space of the end-effector (EEF) does not map into a closed curve in the joint space. This results in nonrepetitive motion in the joint space, even though the EEF motion is repetitive. In this article, we present a solution for the noncyclicity problem in the DLS method. The proposed scheme was successfully tested both in simulation (9 DoF robot) and on a real robotic manipulator (7 DoF robot)
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