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See detail2D Tool-Path Generation Method for Multi-Axis Milling Machine using ToF camera
Ahmad, Rafiq UL; Plapper, Peter UL

Scientific Conference (2014, September 12)

Multi-axis machines are known for their precise production of complex parts, where multi-tool are working in the same area or static workpiece support or clamping parts, may cause collision problems. It ... [more ▼]

Multi-axis machines are known for their precise production of complex parts, where multi-tool are working in the same area or static workpiece support or clamping parts, may cause collision problems. It is therefore necessary to identify potential collision risks and avoid them in an efficient way, which may cause production stops and machinery damage. This research study has been focusing on safe non-functional (rapid) tool-path generation for multi-axis milling machine, where no efficient automatic collision avoidance solution exists (in the literature). A 3D Time of Flight (TOF) camera attached into the machine will be able to sense any unwanted situation in the manufacturing environment and provide rapid and automatic solution to detect and avoid collisions for safe tool movements during production. In the presence of obstacles, the proposed approach will provide decisions regarding tool-path correction and improvement automatically. The proposed algorithm based on 3D vision concept is also able to take into account unknown obstacle shape, size during production but dynamic aspects of the scene will be treated in future. The concept presented take into account the 3D information from the scene for traversal safe tool-paths generation for a static environment as an initial application, which will be adapted to more complex real machining scenarios by integrating it with STEP-NC technology in future. [less ▲]

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See detailRobust Direct Adaptive Fuzzy Control of Switched Constrained Manipulators with Unknown Dynamics
Jasim, Ibrahim UL; Plapper, Peter UL

in Joint 45th International Symposium on Robotics (ISR 2014) and 8th German Conference on Robotics (ROBOTIK 2014) (2014, June 02)

In this article, we address the problem of controlling robots with arbitrarily-switched constraints and unknown dynamics. Switching between different constraints of a robot would result in a switched ... [more ▼]

In this article, we address the problem of controlling robots with arbitrarily-switched constraints and unknown dynamics. Switching between different constraints of a robot would result in a switched nonlinear system that does not inherit the behavior of its individual subsystems. In order to guarantee stable performance of robots with arbitrarily switched constraints and unknown dynamics, we propose a Robust Adaptive Fuzzy Control (RAFC) strategy that can guarantee global stable performance under such challenging conditions. The suggested control strategy relies on the synergy of the Sliding Mode Control (SMC) that adds robustness against possible dynamics parameters drift, finding a Common Lyapunov Function (CLF) that guarantees stability under arbitrary constraints switching, and Direct Adaptive Fuzzy System (DAFS) that relaxes the need for knowing the precise robot dynamics. Experiments are performed on a KUKA Lightweight Robot (LWR) doing camshaft caps assembly of an automotive powertrain. The given robotic assembly process falls in the category of switched constrained robots and the efficiency of the suggested RAFC strategy in controlling such a robotic task will be shown. [less ▲]

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See detailRobust Direct Adaptive Fuzzy Control of Flexible Joints Robots with Time-Varying Stiffness/Damping Parameters
Jasim, Ibrahim UL; Plapper, Peter UL

in Joint 45th International Symposium on Robotics (ISR 2014) and 8th German Conference on Robotics (ROBOTIK 2014) (2014, June 02)

In this article, we address the problem of controlling unknown flexible-joint robots with unknown time-varying stiffness and damping parameters. We propose a Robust Direct Adaptive Fuzzy Control (RDAFC ... [more ▼]

In this article, we address the problem of controlling unknown flexible-joint robots with unknown time-varying stiffness and damping parameters. We propose a Robust Direct Adaptive Fuzzy Control (RDAFC) strategy that accommodates the dynamics anonymity and joints stiffness/damping variations. The RDAFC strategy relies on the synergy of the concepts of fuzzy logic approximation and the Sliding Mode Control (SMC). The fuzzy logic approximation relaxes the need for knowing the robot dynamics and the SMC accommodates the parameters variations. We also modify the RDAFC strategy to be suited to the KUKA Lightweight Robot (LWR) and propose a control strategy that can accommodates dynamics anonymity, uncertainty and joints elasticity variations. Experimental results are performed on a KUKA LWR moving in free space with its joints stiffness and damping vary with time in sine and cosine waveforms respectively. From the experiments, we can see that excellent tracking performance is obtained when using the RDAFC strategy despite the joints elasticity parameters time-variance and the robot dynamics unavailability. [less ▲]

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See detailContact-State Recognition of Compliant Motion Robots Using Expectation Maximization-Based Gaussian Mixtures
Jasim, Ibrahim UL; Plapper, Peter UL

in Joint 45th International Symposium on Robotics (ISR 2014) and 8th German Conference on Robotics (ROBOTIK 2014) (2014, June 02)

In this article, we address the problem of Contact-State (CS) recognition for force-controlled robotic tasks. At first, the wrench (Cartesian forces and torques) and pose (Cartesian position and ... [more ▼]

In this article, we address the problem of Contact-State (CS) recognition for force-controlled robotic tasks. At first, the wrench (Cartesian forces and torques) and pose (Cartesian position and orientation) signals of the manipulated object, in different Contact Formations (CFs) of a task, are collected. Then in the framework of the Bayesian classification, the Expectation Maximization-based Gaussian Mixtures Model (EM-GMM) is used in building efficient CFs classifiers. The use of the EM-GMM in developing the captured signals models accommodates possible signals non-stationarity, i.e. signals abnormal distribution, and enhanced recognition performance would be resulted. Experiments are performed on a KUKA Lightweight Robot (LWR) doing the cube-in-corner assembly task, which is a rigid cube object interacting with an environment composed of three orthogonal planes, and different CFs are considered. From the experimental results, the EM-GMM is shown to have an excellent recognition performance with an enhanced computational time. In order to compare the EM-GMM with the available CF recognition schemes, we developed the corresponding CF classifiers using the Gravitational Search-Fuzzy Clustering Algorithm (GS-FCA), Stochastic Gradient Boosting (SGB), and the Conventional Fuzzy Classifier(CFC) approaches. From the comparison results it is obvious that the EM-GMM scheme is outperforming the rest. [less ▲]

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See detailElectrical performance of laser braze-welded aluminum–copper interconnects
Solchenbach, Tobias UL; Plapper, Peter UL; Cai, Wayne

in Journal of Manufacturing Processes (2014), 16(2), 183-189

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See detailLaser Assisted Joining of Hybrid Polyamide-aluminum Structures
Lamberti, Christian UL; Solchenbach, Tobias UL; Plapper, Peter UL et al

in Physics Procedia (2014), 56(0), 845-853

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See detailContact-state modeling of robotic assembly tasks using Gaussian mixture models
Ibrahim, Jasim; Plapper, Peter UL

in Procedia CIRP (2014), 23

This article addresses the Contact-State (CS) modeling problem for the force-controlled robotic peg-in-hole assembly tasks. The wrench (Cartesian forces and torques) and pose (Cartesian position and ... [more ▼]

This article addresses the Contact-State (CS) modeling problem for the force-controlled robotic peg-in-hole assembly tasks. The wrench (Cartesian forces and torques) and pose (Cartesian position and orientation) signals, of the manipulated object, are captured for different phases of the robotic assembly task. Those signals are utilized in building a CS model for each phase. Gaussian Mixture Models (GMM) is employed in building the likelihood of each signal and Expectation Maximization (EM) is used in finding the GMM parameters. Experiments are performed on a KUKA Lightweight Robot (LWR) doing camshaft caps assembly of an automotive powertrain. Comparisons are also performed with the available assembly modeling schemes, and the superiority of the EM-GMM scheme is shown with a reduced computational time. [less ▲]

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See detailContact-state modeling of robotic assembly tasks using Gaussian mixture models
Jasim, Ibrahim UL; Plapper, Peter UL

in Procedia CIRP (2014), 23

This article addresses the Contact-State (CS) modeling problem for the force-controlled robotic peg-in-hole assembly tasks. The wrench (Cartesian forces and torques) and pose (Cartesian position and ... [more ▼]

This article addresses the Contact-State (CS) modeling problem for the force-controlled robotic peg-in-hole assembly tasks. The wrench (Cartesian forces and torques) and pose (Cartesian position and orientation) signals, of the manipulated object, are captured for different phases of the robotic assembly task. Those signals are utilized in building a CS model for each phase. Gaussian Mixture Models (GMM) is employed in building the likelihood of each signal and Expectation Maximization (EM) is used in finding the GMM parameters. Experiments are performed on a KUKA Lightweight Robot (LWR) doing camshaft caps assembly of an automotive powertrain. Comparisons are also performed with the available assembly modeling schemes, and the superiority of the EM-GMM scheme is shown with a reduced computational time. [less ▲]

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See detailPosition identification in force-guided peg-in-hole assembly tasks
Ibrahim, Jasim; Plapper, Peter UL; Voos, Holger UL

in Procedia CIRP (2014), 23

Position uncertainty is inevitable in many force-guided robotic assembly tasks. Such uncertainty can cause a significant delay, extra energy expenditure, and may even results in detriments to the mated ... [more ▼]

Position uncertainty is inevitable in many force-guided robotic assembly tasks. Such uncertainty can cause a significant delay, extra energy expenditure, and may even results in detriments to the mated parts or the robot itself. This article suggests a strategy for identifying the accurate hole position in force-guided robotic peg-in-hole assembly tasks through employing only the captured wrench (the Cartesian forces and torques) signals of the manipulated. In the framework of using the Contact-State (CS) modeling for such robotic tasks, the identification of the hole position is realized through detecting the CS that corresponds for the phase of the peg-on-hole, that is the phase in which the peg is located precisely on the hole. Expectation Maximization-based Gaussian Mixtures Model (EM-GMM) CS modeling scheme is employed in detecting the CS corresponding for the peg-on-hole phase. Only the wrench signals are used in modeling and detecting the phases of the assembly process. The considered peg-in-hole assembly process starts from free space and as soon as the peg touches the environment with missing the hole, a spiral search path is followed that would survey the whole environment surface. When the CS of the peg-on-hole is detected, the hole position is identified. Experiments are conducted on a KUKA Lightweight Robot (LWR) doing typical peg-in-hole assembly tasks. Multiple hole positions are considered and excellent performance of the proposed identification strategy is shown. [less ▲]

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See detailThermal and electrical aging of laser braze-welded aluminum–copper interconnects
Solchenbach, Tobias UL; Plapper, Peter UL; Greger, Manfred UL et al

in Translational Materials Research (2014), 1(1), 015001

Aluminum–copper (Al–Cu) interconnects are of great interest for a variety of electrical applications, such as lithium-ion batteries. In this paper, the effects of thermal and electrical aging on the ... [more ▼]

Aluminum–copper (Al–Cu) interconnects are of great interest for a variety of electrical applications, such as lithium-ion batteries. In this paper, the effects of thermal and electrical aging on the intermetallic compound growth of laser braze-welded Al–Cu interconnects are reported. Thermal aging was studied in a temperature range from 200 to 500 °C for durations between 1 and 120 h. Electrical aging was studied with 200 A direct current application with different polarities and durations between 1 and 24 h. The formation of intermetallic compounds was found to be dependent on the type of aging and, for electrical aging, on the polarity of the current. The growth of intermetallic compounds under the influence of the electric current was distinctly higher than for thermal annealing conditions. The formation of voids at the transition between intermetallic compounds indicates that electromigration may be the main driving force for the accelerated intermetallic growth. [less ▲]

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See detailContact-State Monitoring of Force-Guided Robotic Assembly Tasks Using Expectation Maximization-based Gaussian Mixtures Models
Jasim, Ibrahim UL; Plapper, Peter UL

in International Journal of Advanced Manufacturing Technology (2014), 73(5), 623-633

This article addresses the problem of Contact-State (CS) monitoring for peg-in-hole force-controlled robotic assembly tasks. In order to perform such a monitoring target, the wrench (Cartesian forces and ... [more ▼]

This article addresses the problem of Contact-State (CS) monitoring for peg-in-hole force-controlled robotic assembly tasks. In order to perform such a monitoring target, the wrench (Cartesian forces and torques) and pose (Cartesian position and orientation) signals of the manipulated object are firstly captured for different CS's of the object (peg) with respect to the environment including the hole. The captured signals are employed in building a model (a recognizer) for each CS and in the framework of pattern classification the CS monitoring would be addressed. It will be shown that the captured signals are non-stationary, i.e. they have non-normal distribution that would result in performance degradation if using the available monitoring approaches. In this article, the concept of the Gaussian Mixtures Models (GMM) is used in building the likelihood of each signal and the Expectation Maximization (EM) algorithm is employed in finding the GMM parameters. The use of the GMM would accommodate the signals non-stationary behavior and the EM algorithm would guarantee the estimation of the optimal parameters set of the GMM for each signal and hence the modeling accuracy would be significantly enhanced. In order to see the performance of the suggested CS monitoring scheme, we installed a test stand that is composed of a KUKA Lightweight Robot (LWR) doing a typical peg-in-hole tasks. Two experiments are considered; in the first experiment we use the EM-GMM in monitoring a typical peg-in-hole robotic assembly process and in the second experiment we consider the robotic assembly of camshaft caps assembly of an automotive powertrain and use the EM-GMM in monitoring its CS's. For both experiments, the excellent monitoring performance will be shown. Furthermore, we compare the performance of the EM-GMM with that obtained when using available CS monitoring approaches. Classification Success Rate (CSR) and computational time will be considered as comparison indices and the EM-GMM will be shown to have a superior CSR performance with reduced a computational time. [less ▲]

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See detailStable Robust Adaptive Control of Robotic Manipulators with Switched Constraints
Jasim, Ibrahim UL; Plapper, Peter UL

in Proceedings of the 2013 IEEE International Conference on Mechatronics and Automation, IEEE ICMA 2013 (2013, August)

In this paper, the problem of controlling switched constrained robotic manipulators is addressed. Switched constrained robots are those robots interacting with multiple switched constraints. We start our ... [more ▼]

In this paper, the problem of controlling switched constrained robotic manipulators is addressed. Switched constrained robots are those robots interacting with multiple switched constraints. We start our control algorithm with suggesting a sliding mode controller that is proved to provide stable system performance. However, the bounds of the functions, on each link, caused from the constraints are assumed to be known. Then an adaptive sliding mode control strategy is suggested that relaxes the need for knowing the bounds of the constraints functions with guaranteeing global stable performance of the given switched constrained robotic system. Finally, we complement the control strategy above through deriving an improved robust adaptive control scheme that is proved to give a stable performance with reduced chattering. All of the three stages of the suggested control strategy are derived through finding a common Lyapunov function that can stabilize all of the subsystems for the overall switched system. Simulation is carried out for a two link robotic manipulator interacting with two switched constraints. From the simulation results we can see the excellent tracking performance and the high efficiency of the suggested control strategy in controlling switched constrained robotic systems. [less ▲]

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See detailAdaptive Sliding Mode Control of Switched Constrained Robotic Manipulators
Jasim, Ibrahim UL; Plapper, Peter UL

in 2013 IEEE International Conference on Industrial Informatics, Bochum 28-30 July 2013 (2013, July)

In this paper, we address the control problem of a constrained robotic manipulators with their constraints continuously switched from one to another. Such a switching in the constraints causes a switching ... [more ▼]

In this paper, we address the control problem of a constrained robotic manipulators with their constraints continuously switched from one to another. Such a switching in the constraints causes a switching function to be inserted in the equation of the robot dynamics which may cause transient instability for the overall system. Two robust control strategies are presented in this paper to handle such switched robotic systems. In the first strategy, we assume that the bounds of the constraints are known. A sliding mode stabilizing controller is developed that can guarantee global stable performance of the given robotic system. In the second one, we relax the assumption of knowing the constraints bounds through deriving update laws for those bounds and new control actions that can guarantee global stable performance under such switching constraints. Simulation is performed for a two link robotic system having two switching constraints. The results obtained from the simulation verify the efficacy of the suggested control strategy. [less ▲]

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See detailHuman Error Identification in Programming by Demonstration of Compliant Motion Robotic Tasks
Jasim, Ibrahim UL; Plapper, Peter UL

in 2013 IEEE International Conference on Fuzzy Systems (FUZZ-IEEE 2013), Hyderabad 7-10 July 2013 (2013, July)

In this paper, we suggest a scheme for error identification in human skills transfer when using the Programming by Demonstration (PbD) in adding a set of skills from a human operator to the force ... [more ▼]

In this paper, we suggest a scheme for error identification in human skills transfer when using the Programming by Demonstration (PbD) in adding a set of skills from a human operator to the force- controlled robotic tasks. Such errors in human skills transfer is majorly caused from the difficulty of properly synchronizing the human and machine responses. Based on the captured Cartesian forces and torques signals of the manipulated object, we present an approach of identifying the errors stemmed from human wrong skills transfer in a PbD process. The scheme is composed of using the Gravitational Search- Fuzzy Clustering Algorithm (GS-FSA) in finding the centroid of the captured forces and torques signals for each Contact Formation (CF). Then using a distance- based outlier identification approach along with the centroid of each signal, the human errors can be identified in the framework of data outlier identification. In order to validate the approach, a test stand, composed of a KUKA Light Weight Robot manipulating a rigid cube object, is built. The manipulated object is assumed to interact with an environment composed of three orthogonal planes. Error identification for two case studies will be considered and other cases can be dealt with in a similar manner. From the experimental results, excellent human error identification is shown when using the suggested approach. [less ▲]

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See detailT-S Fuzzy Contact State Recognition for Compliant Motion Robotic Tasks Using Gravitational Search-Based Clustering Algorithm
Jasim, Ibrahim UL; Plapper, Peter UL

in 2013 IEEE International Conference on Fuzzy Systems (FUZZ-IEEE 2013) (2013, July)

In this paper, we address the problem of contact state recognition for compliant motion robotic systems. The wrench (Cartesian forces and torques) and pose (position and orientation) of the manipulated ... [more ▼]

In this paper, we address the problem of contact state recognition for compliant motion robotic systems. The wrench (Cartesian forces and torques) and pose (position and orientation) of the manipulated object in different Contact Formations (CFs) are firstly captured during a certain task execution. Then for each CF, we develop an efficient Takagi- Sugeno (T-S) fuzzy inference system that can model that specific CF using the available input (wrench and pose) - output (the desired model output for each CF) data. The antecedent part parameters are computed using the Gravitational Search- based Fuzzy Clustering Algorithm (GS- FCA) and the consequent parts parameters are tuned by the Least Mean Square (LMS). Excellent mapping and hence recognition capabilities can be expected from the suggested scheme. In order to validate the approach; experimental test stand is built which is composed of a KUKA Light Weight Robot (LWR) manipulating a cube rigid object that interacts with an environment composed of three orthogonal planes. The manipulated object is rigidly attached to the robot arm. The robot is programmed, by a human operator, to move in different CFs and for each CF, the wrench and pose readings are captured via the Fast Research Interface (FRI) available at the KUKA LWR. Using the suggested approach, excellent modeling is obtained for different CFs during the robot task execution. A comparison with the available CF recognition approaches is also performed and the superiority of the suggested scheme is shown. [less ▲]

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See detailCombined Laser Beam Braze-Welding Process for Fluxless Al-Cu Connections
Solchenbach, Tobias UL; Plapper, Peter UL

in PROCEEDINGS INTERNATIONAL CONFERENCE ON COMPETITIVE MANUFACTURING (2013, January 31)

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See detailCombined Laser Beam Braze-Welding Process for Fluxless Al-Cu Connections
Solchenbach, Tobias UL; Plapper, Peter UL

in Dimitrov, Dimiter; Schutte, Corne (Eds.) PROCEDINGS International Conference on competitive Manufacturing, COMA 13 (2013, January)

A combined laser beam welding and brazing process for Al-Cu connections in overlap configuration is investigated. Aluminium and copper for electric and electronic application is used for experiments ... [more ▼]

A combined laser beam welding and brazing process for Al-Cu connections in overlap configuration is investigated. Aluminium and copper for electric and electronic application is used for experiments without surface treatment or activation, e.g. by flux. Although Al and Cu have been considered as “not weldable”, the possibility of a thermal joining process, i.e., the weld-brazing, was proved. The inevitable formation of intermetallic compounds at the interfacial region was reduced to less than 4 µm. Shear strength up to 51 MPa was achieved. A detailed fracture analysis has shown that the copper-rich intermetallic phase is the metallurgical weakest point due to the distinctive brittleness, even though the Al-rich Cu-phase is several times thicker. [less ▲]

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See detailMechanical Characteristics of Laser Braze-Welded Aluminium-Copper Connections
Solchenbach, Tobias UL; Plapper, Peter UL

in Optics & Laser Technology (2013)

Abstract The mechanical characteristics of dissimilar Al-Cu connections, joined by a novel, robust laser braze-welding process are reported. A ber laser is used in combination with a 2D galvoscanner to ... [more ▼]

Abstract The mechanical characteristics of dissimilar Al-Cu connections, joined by a novel, robust laser braze-welding process are reported. A ber laser is used in combination with a 2D galvoscanner to provide spatial power modulation by superposed circular beam oscillation. With the help of statistical experimental design, a broad range of processing parameters has been inves- tigated in order to understand their e ects on the joint characteristics. A maximum shear strength of 121 MPa has been detected within the scope of the experiments. [less ▲]

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See detailMechanical Properties of Laser Braze-Welded Al-Cu connections
Solchenbach, Tobias UL; Plapper, Peter UL

in Mechanical Properties of Laser Braze-Welded Al-Cu connections (2012, November)

The paper describes an innovative, laser based joining method for dissimilar Al-Cu connections. The main objective is the improvement of the mechanical and electrical properties of the joints.

Detailed reference viewed: 91 (11 UL)