This paper presents a novel parametrization strategy for optimal contouring control of flexible feed drives. The aim of the new strategy is to maximize the structural damping of the drive and ...counteract the deformations of the structure. Using a simplified flexible multibody model, the analytical relationships for the design of velocity and position control gains were derived. This results in a controller bandwidth increase of up to 20% compared to the previous state-of-the-art in parametrization of standard cascaded controllers. Through analytical and numerical calculations, it was demonstrated that such an increase is feasible without a decrease in structural damping if the position and velocity controller gains are both considered. Furthermore, it is shown that the ratio between the position and velocity loop gains influences the quasistatic deformation between the encoder and tool center point (TCP). A formula for the optimal choice of the ratio was derived to compensate for the error. This leads to a new straightforward step-by-step approach for axis controller setting, which is then applied to a test bench and its simulation model. It can be shown that the new parametrization strategy leads to a significant reduction in path error at the TCP. Importantly, the analytical approach should simplify the task of setting up a standard cascaded controller significantly by avoiding time-consuming iterations.
Mechatronic structures deform under static and dynamic loads. These deformations lead to deviations at the tool center point (TCP), affecting the reachable accuracy and/or productivity of the ...machines. The scope of this work is the comparison of calculations and measurements of different static and dynamic errors on a dynamic test bench. A reduced-order modelling approach is applied for the test bench modelling. It uses a combination of modal condensation and moment-matching methods with Krylov subspaces. The different modelling steps and requirements are presented. The same model is used for all static and dynamic evaluations presented within this paper. Static deformations, leading to roll and pitch deviations at the TCP of the test bench structure, are simulated using the described modelling methodology and validated by inclination measurements. The modal behavior of the system is investigated by calculation and compared to the measurements at a single axes position. The spatial change of the frequency response functions of the modelled system is investigated further, by calculation and measurement of the velocity open-loop FRFs of one axis for different machine configurations. In addition, a transient trajectory simulation is performed and compared to the Heidenhain KGM and encoder measurements. The large variety of comparisons shows the efficient applicability of the modelling environment MORe.
The targeted placement of selected carbon nanotubes is associated with low throughput rates. Hence, this paper presents a novel stage design for the fully automatic assembly of carbon nanotube ...field-effect transistors (CNTFETs) via mechanical dry transfer. It constitutes the core module of an assembly machine for the precise deployment of nanotubes onto a prefabricated wafer. The mechanical dry transfer approach allows high level of carbon nanotube selectivity with the aim of enabling a high-volume fabrication of ultra-clean devices. The previous production rate of such ultra-clean devices is less than one per hour, which offers a high potential for improvement. The stage consists of a parallel kinematic mechanism (PKM) with 3 degrees of freedom (X2Y2C1) carrying two additional stacked axes (Z1C2). The PKM is suspended on a vacuum preloaded aerostatic bearing, voice coil motors (VCM) and flexure hinges. Together with a combination of high precision and resolution touch probe measurement systems close to its tool center point (TCP), high accuracy and low settling time can be achieved. Based on realistic manufacturing tolerances, a sensitivity analysis of the mechanism’s pseudo rigid body model (PRBM) suggests a theoretical closed-loop error below 0.15μm over the entire XY workspace of 20mm×2.8mm. Measurements of positioning motions show that the settling time can be decreased by the compensation of friction resistances inside the internal bearings of the VCMs.
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•Parallel kinematic micromanipulator with novel axis configuration.•Non-monolithic flexure hinge/voice coil combination.•Sensitivity analysis for the accuracy assessment of the manipulator.•Significant reduction of overshoot and settling time.
•Semi-analytical approach for determination of load sharing of a face-gear drive.•Assessment of static transmission error, flank contact pressure and tooth root stress.•Comparison of semi-analytical ...approach with FEM contact analysis.
The present manuscript expands on a procedure developed to calculate load sharing, transmission characteristics, tooth root stress and the flank contact pressure in face-gear drives. On the one hand the procedure uses the analytical determination of the contact path for meshing of rigid gears including the dimensions, and directions of the contact ellipses based on Hertzian theory of elastic contact. On the other hand it uses the determination of the load-dependant compliance of a pair of teeth by finite element analysis. The combination of these two calculation methods / approaches renders the finite element contact analysis unnecessary thus significantly shortening the required computation time. The exact geometric representation of the tooth flanks for the finite element analysis is also not required. This not only avoids a greater preprocessing effort but also enables an efficient automation of the procedure. All steps of this procedure are described in depth in this manuscript. The accuracy of the proposed semi-analytical approach is validated through a direct comparison with an FEM contact analysis carried out as an example for a face-gear drive.
The demands on laser cutting machine tools are increasing constantly. In this paper, we focus on increasing productivity while minimizing the deterioration of part quality. Without specific ...countermeasures, increasing the dynamic settings leads to larger dynamic-induced contour errors of the workpiece. Software-based methods offer potential to improve the contour tracking under varying dynamic settings without the need for a mechanical redesign of the machine tool. Four such methods, which rely on different combinations of model- and/or sensor-based setpoint compensation, are implemented and tested on a laser cutting machine tool. A comparison with respect to productivity and contour accuracy of cut parts is presented, and the complexity of development as well as deployment for production are discussed.
Dynamic, quasi-static and motion control deviations lead to nonlinear but systematic tracking errors. It is shown that these errors can be reduced significantly by adjusting the set points using an ...optimization based iterative learning approach. This method uses either values obtained from internal encoders or alternatively tool center point measurements. The approach is presented, discussed and validated using simulation and measurement results.
Accurate finite element machine modelling is typically connected with high computational costs. For this reason, machine structures are usually simplified or analysed only partially. In this paper, ...an efficient machine modelling technique is presented. It makes use of modal condensation and Krylov subspace model order reduction techniques for Finite-Element-models and Fourier element coupling for moving interfaces. The resulting model is stated to be accurate statically and below a definable frequency. Especially the benefit of having an accurate low order static and dynamic machine model for grinding machine and process simulation is outlined. This enables a full size transient simulation without simplification or omission of potentially important machine components. The modelling methodology is applied to a large and complex test rig for high performance dry grinding. This test rig is used to emulate the railway grinding process, where low frequency deviations are acoustically most relevant. In order to be later used for transient grinding simulations, all test rig components are modelled and assembled. For the validation of the model, its modes and mode-shapes are compared to the results of an experimental modal analysis performed on the real test rig. TCP frequency response functions are further compared between measurement and simulation. The potential use of the model for surface roughness and waviness simulations is shortly implied.
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