Robot-sensor synchronization for real-time seamtracking in robotic laser welding

The accuracy requirements of laser welding put high demands on the manipulator that is used. To use industrial six-axis robots for manipulating the laser welding optics, sensors measuring the seam trajectory close to the focal spot are required to meet the accuracy demands. When the measurements are taken while the robot is moving, it is essential that they are synchronized with the robot motion. This paper presents a synchronization mechanism between a seam-tracking sensor and an industrial 6-axis robot, which uses Ethernet-based UDP communication. Experimental validation is carried out to determine the accuracy of the proposed synchronization mechanism. Furthermore, a new control architecture, called trajectory-based control is presented, which embeds the synchronization method and allows various sensor-based applications like teaching of a seam trajectory with a moving robot and real-time seam-tracking during laser welding

Robust process-controller for Nd:YAG welding

A robust process-controller was developed which maintains a fully penetrated weld. This feedback-controller is robust for various process disturbances that may occur, like variations in sheet thickness, welding velocity, focal position, shielding gas variations, etc. The signals from an optical sensor are used to design a so-called "switching" controller, which enables fully penetrated welding at a minimum amount of laser power. It is shown that the working principle of the controller is applicable to different material types, more specific different steels and stainless steels. Experiments have been carried out to show the ability to cope with varying sheet thickness and\ud welding velocity on FeP04 mild steel. Furthermore a method is described which can be used to easily find a good set of control parameters from a single identification experiment

Resolving hydrogen atoms at metal-metal hydride interfaces

Hydrogen as a fuel can be stored safely with high volumetric density in metals. It can, however, also be detrimental to metals causing embrittlement. Understanding fundamental behavior of hydrogen at atomic scale is key to improve the properties of metal-metal hydride systems. However, currently, there is no robust technique capable of visualizing hydrogen atoms. Here, we demonstrate that hydrogen atoms can be imaged unprecedentedly with integrated differential phase contrast, a recently developed technique performed in a scanning transmission electron microscope. Images of the titanium-titanium monohydride interface reveal remarkable stability of the hydride phase, originating from the interplay between compressive stress and interfacial coherence. We also uncovered, thirty years after three models were proposed, which one describes the position of the hydrogen atoms with respect to the interface. Our work enables novel research on hydrides and is extendable to all materials containing light and heavy elements, including oxides, nitrides, carbides and borides

A complex-like calculus for spherical vectorfields

First, R^{1+d}, d in N, is turned into an algebra by mimicing the usual complex multiplication. Indeed the special case d = 1 reproduces C. For d > 1 the considered algebra is commutative, but non-associative and even non-alternative. Next, the Dijkhuis class of mappings (’vectorfields’) R^{1+d} ¿ R^{1+d}, suggested by C.G. Dijkhuis for d=3, d=7, is introduced. This special class is then fully characterized in terms of analytic functions of one complex variable. Finally, this characterization enables to show easily that the Dijkhuis-class is closed under pointwise R^{d+1}-multiplication: It is a commutative and associative algebra of vector fields. Previously it had not been observed that the Dijkhuis-class only contains vectorfields with a ’time-dependent’ spherical symmetry. Such disappointment was to be expected! The class of functions which are differentiable with respect to the algebraic structure, that we impose on R^{1+d}, contains only linear functions if d > 1. The Dijkhuis-class does not appear this way either! In our treatment neither quaternions nor octonions play a role

A complex-like calculus for spherical vectorfields

First, R^{1+d}, d in N, is turned into an algebra by mimicing the usual complex multiplication. Indeed the special case d = 1 reproduces C. For d > 1 the considered algebra is commutative, but non-associative and even non-alternative. Next, the Dijkhuis class of mappings (’vectorfields’) R^{1+d} ¿ R^{1+d}, suggested by C.G. Dijkhuis for d=3, d=7, is introduced. This special class is then fully characterized in terms of analytic functions of one complex variable. Finally, this characterization enables to show easily that the Dijkhuis-class is closed under pointwise R^{d+1}-multiplication: It is a commutative and associative algebra of vector fields. Previously it had not been observed that the Dijkhuis-class only contains vectorfields with a ’time-dependent’ spherical symmetry. Such disappointment was to be expected! The class of functions which are differentiable with respect to the algebraic structure, that we impose on R^{1+d}, contains only linear functions if d > 1. The Dijkhuis-class does not appear this way either! In our treatment neither quaternions nor octonions play a role

Tensors and second quantization

Starting from a pair of vector spaces (formula) an inner product space and (formula), the space of linear mappings (formula), we construct a six-tuple (formula). Here (formula) is again an inner product space and (formula) the space of its linear mappings. It is required that (formula), as linear subspaces. (formula) Further, (formula) and (formula) denotes a lifting map (formula) such that, whenever (formula) solves an evolution equation (formula) then any product of operator valued functions (formula) solves the associated commutator equation in (formula), (formula) Furthermore, (formula). We also note that (formula) represents the state of k identical systems ’living apart together’. Cf. the free field ’formalism’ in physics. Such constructions can be realized in many different ways (section 2). However in Quantum Field Theory one requires additional relations between the creation operator C and its adjoint (formula), the annihilation operator. These are the so called Canonical (Anti-)Commutation Relations, (section 3). Here, unlike in books on theoretical physics, the combinatorial aspects of those 1This note is meant to be Appendix K in the lecture notes ’Tensorrekening en Differentiaalmeetkunde’. restrictions are dealt with in full detail. Annihilation/Creation operators don’t grow on trees! However, apart from the way of presentation, nothing new is claimed here. This note is completely algebraic. For topological extensions of the maps C; A to distribution spaces we refer to Part III in [EG], where a mathematical interpretation of Dirac’s formalism has been presented