We present a novel method for rapid and flexible laser marking and engraving of tilted, curved and freeform work-piece surfaces. The method is based on integrating a three-dimensional (3D) laser ...measurement system into a 3D laser marking system. We use the same laser source and optics for measurement and processing with a minimum of additional hardware components. A low power CW laser regime is used to measure the 3D shape of a work-piece surface while a high-peak power-pulsed laser regime is used for processing. The acquired 3D surface data are used to determine the 3D trajectory of the processing beam focus. Neither the 3D shape of the work-piece nor its orientation needs to be known in advance as long as the processed surface lies within the working range of the 3D laser processing system. This eliminates the need for exact work-piece positioning before processing and substantially improves processing flexibility (allowing, e.g. variations in work-piece shape or/and orientation from mark to mark). This paper discusses key issues concerning an implementation of the method and presents typical examples of markings and engravings, which demonstrate the advantages of the method with respect to the existing industrial 2D and 3D laser marking and engraving methods. The method can also be applied to flexible laser structuring and microprocessing of curved surfaces.
►A novel method for rapid and flexible laser marking and engraving has been developed. ►A 3D laser measurement system is integrated into a 3D laser marking system. ►Tilted, curved and freeform work-piece surfaces can be processed. ►Neither the 3D shape of the work-piece nor its orientation need to be known in advance. ►Key issues about implementation of the method are discussed.
•Modeling using Green’s function formalism and streamlined Huygens’ principle.•The model incorporates spatial distributions of source and sensor sensitivity.•A statistically simplified area-to-area ...ultrasound transfer function was developed.•Uniform, Gaussian and annular source ultrasonic waveforms are simulated.•Thus-simulated waveforms match the measurements more closely than the point model.
The near-field, surface-displacement waveforms in plates are modeled using interwoven concepts of Green’s function formalism and streamlined Huygens’ principle. Green’s functions resemble the building blocks of the sought displacement waveform, superimposed and weighted according to the simplified distribution. The approach incorporates an arbitrary circular spatial source distribution and an arbitrary circular spatial sensitivity in the area probed by the sensor. The displacement histories for uniform, Gaussian and annular normal-force source distributions and the uniform spatial sensor sensitivity are calculated, and the corresponding weight distributions are compared. To demonstrate the applicability of the developed scheme, measurements of laser ultrasound induced solely by the radiation pressure are compared with the calculated waveforms. The ultrasound is induced by laser pulse reflection from the mirror-surface of a glass plate. The measurements show excellent agreement not only with respect to various wave-arrivals but also in the shape of each arrival. Their shape depends on the beam profile of the excitation laser pulse and its corresponding spatial normal-force distribution.
In this paper we report on a theoretical and experimental study of the steady-state response, transient response and efficiency of a thermal management system. We compare two alternative designs ...based on thermo-electric modules, the role of which is to control the temperature of the laser-diode pumping system for advanced fiber lasers. The performances of a standard pulse-width modulation controller and a variable-voltage controller were tested on a reference thermal management system. An experimental facility and a numerical model were set up, with the system response to various load conditions measured as well as numerically simulated. The results show that the design of the thermal management system based on the variable-voltage controller offers a significant performance advantage over the pulse-width modulation design.
•We have compared the performance of two alternative temperature controllers.•The pulse-width modulation design was compared with a variable-voltage design.•A significant difference in the duration of the transient response was observed.•The variable-voltage design offers a reduced steady-state power consumption.
We report on the successful realization of a contactless, non-perturbing, displacement-measuring system for characterizing the surface roughness of polymer materials used in tribological ...applications. A single, time-dependent, scalar value, dubbed the collective micro-asperity deformation, is extracted from the normal-displacement measurements of normally loaded polymer samples. The displacement measurements with a sub-nanometer resolution are obtained with a homodyne quadrature laser interferometer. The measured collective micro-asperity deformation is critical for a determination of the real contact area and thus for the realistic contact conditions in tribological applications. The designed measuring system senses both the bulk creep as well as the micro-asperity creep occurring at the roughness peaks. The final results of our experimental measurements are three time-dependent values of the collective micro-asperity deformation for the three selected surface roughnesses. These values can be directly compared to theoretical deformation curves, which can be derived using existing real-contact-area models.
This article examines the influence of incident angle, object colour and measurement distance on the computer numerically controlled laser scanning process. To determine the physical background of ...these influences, the operation of the triangulation sensor, the surface reflection and the colour properties of the measured object were analysed. The various influences and their physical background are explained by using a test-measurement setup, which makes it possible to investigate a specific influencing factor. The article concludes with several guidelines that should be followed in order to obtain better measurement results.
Optodynamic interaction between a laser pulse and the surface of an opaque, solid elastic object produces transient waves that propagate and reverberate within the object. They can be, in general, ...categorized into three distinctive types which are all formed through different mechanisms: ablation-induced waves, light-pressure-induced waves, and thermoelastic waves. In this paper, out-of-plane displacements of such waves are simulated at the epicentral position on the opposite side of an extended plane-parallel elastic plate. Wave propagation is mathematically described by Green’s transfer functions convolved with suitable time profiles of the incoming laser pulses. The simulated size of the circularly symmetric laser-illuminated area on the plate surface is varied to show the limit-to-limit transition of the displacement waveforms: from a 2D point source to an infinite 1D source.
The goal of this research is to use the information contained in the mechanisms occurring during the laser tattoo removal process. We simultaneously employed a laser-beam deflection probe (LBDP) to ...measure the shock wave and a camera to detect the plasma radiation, both originating from a high-intensity laser-pulse interaction with a tattoo. The experiments were performed
(skin phantoms),
(marking tattoos on pig skin), and
(professional and amateur decorative tattoos). The LBDP signal includes the information about the energy released during the interaction and indicates textural changes in the skin, which are specific for different skin and tattoo conditions. Using both sensors, we evaluated a measurement of threshold for skin damage and studied the effect of multiple pulses.
results show that a prepulse reduces the interaction strength and that a single strong pulse produces better removal results.
We present an optodynamic measurement of a laser-induced cavitation bubble and its oscillations based on a scanning technique using a laser beam-deflection probe. The deflection of the beam was ...detected with a fast quadrant photodiode which was built into the optical probe. The applied experimental setup enabled us to carry out one- or two-dimensional scanning of the cavitation bubble, automatic control of the experiment, data acquisition and data processing. Shadow photography was used as a comparative method during the experiments.
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