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1

Simplification of the rolling contact-related lifetime calculation of profiled rail guides with a polynomial regression

Staroszyk Danny, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2024

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Vol. 24, No. 1

60--73

EN

The calculation of the lifespan of profile rail guides is an essential part in the design process of machines. Conventional lifespan models yield good results when calculating lifespan values under a homogeneous distribution of individual rolling contact forces on the raceways. In the case of an uneven load distribution, significantly too low lifespan values are calculated, resulting in a considerable loss of lifetime potential. The novel and experimentally validated rolling contact-based lifespan calculation (RCBL) takes the transferred force on each rolling element into account, resulting in more realistic lifespan values that can be up to 4 times higher than those obtained through the classical method. The disadvantage lies in the complex calculation of the necessary individual rolling contact forces, which until now has been done by using extensive finite element models, along with the computationally intensive optimization problem of the RCBL. To overcome these disadvantages, a method is introduced that efficiently calculates the individual rolling contact forces, taking into account all relevant system elasticities, and pre-solves the RCBL for a variety of potential superimposed load combinations. The results are subsequently approximated through an analytical multiparametric polynomial function and can be utilized with the conventional lifespan formula for rolling bearings.

2

Compliant joints with remote centre of compliance for the improvement of the motion accuracy of a gantry stage

Pöhlmann Patrick, Peukert Christoph, Merx Marcel, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2022

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Vol. 22, No. 2

68--79

EN

Gantry stages, which consist of two parallel acting servo drives, are commonly used in machine tools. One drawback of this concept is the crosstalk between both drives, when a stiff mechanical coupling is present. This can lead to a limited bandwidth of the position control or to high reaction forces. One way to overcome these issues is the usage of joints to create an additional degree of freedom, which allows the drives to move independently. The design of these joints as compliant elements offers advantages compared to common rolling bearings, such as low friction and the absence of backlash. Another benefit is the variability in the design of the compliant joints allowing for adjustments to the position of each joint’s centre of compliance. Thus, the position of the resulting pivot, and the transfer matrix between the motion of the drives and the motion at the gantry stage’s tool centre point, change as well. This paper addresses the placement of the joint’s centre of compliance in order to improve motion accuracy. For this purpose, joints with modular arranged compliant links have been designed. The characteristics of the joints and their effect on the behaviour of the gantry stage are compared using analytical investigations as well as experimental results.

3

Thermo-elastic structural analysis of a machine tool using a multi-channel absolute laser interferometer

Deutsch Jessica, Albrecht Tom, Riedel Mirko, Penter Lars, Wiemer Hajo, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2020

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Vol. 20, No. 3

63--75

EN

One of the main errors in the machining accuracy of machine tools is the displacement through thermal induced deformation. Modern design and construction methods aim to optimize the heat flow in the machine to achieve minimum displacement. To enable a further improvement it is essential to know the displacement state of the complete machine structure. However, most measurement methods that are used to capture the influence of a thermal load only measure the displacement of the TCP or individual axes. This paper presents a methodology to capture the complex spatial displacement condition of a state of the art machine tool in one measuring cycle using a multichannel laser interferometer. It describes the development of the measurement model as well as the measurement setup in the workspace of the machine. With measurements according to the presented procedure, it is possible to uncover weak points in the structure of a machine tool and to derive warm-up and cooling strategies.

4

Compliant joints for the improvement of the dynamic behaviour of a gantry stage with direct drives

Pöhlmann Patrick, Peukert Christoph, Merx Marcel, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2020

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Vol. 20, No. 3

17--29

EN

Gantry stages, which consist of two parallel acting servo drives, are commonly used in machine tools. One drawback of this concept is the crosstalk between both drives due to the structural coupling that can cause stability issues and therefore limits the bandwidth of the position control. This paper deals with the development of compliant joints to solve the coupling between the drives. When compared to solutions containing bearings, the advantages of such flexible elements are low friction and the absence of backlash. To adjust the properties of the joints, packages of spring-steel-sheets are used as compliant links. One design aspect of the flexible joints is a low stiffness relating to the rotation around one specific axis, but a high stiffness relating to the other degrees of freedom. With this method, the dynamic behaviour of the gantry stage is modified and the bandwidth of the controllers can be increased. Additionally, by releasing the mechanical coupling of the drives, the reaction forces the actuators have to provide can be reduced. Both systems with flexible and with rigid connecting elements, are analysed by measured frequency response functions.

5

Investigation of local and modal based active vibration control strategies on the example of an elastic system

Peukert Christoph, Pöhlmann Patrick, Merx Marcel, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2019

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Vol. 19, No. 2

32--45

EN

Nowadays, feed axes are often equipped with multiple parallel-acting actuators in order to increase the dynamics of the machine tool. Also, additional actuators for active damping are widely used. Normally, the drives or actuators are controlled independently without consideration for the impact on each other. In contrast, by using the modal space control, the system can be decoupled and the modal control loops can be adjusted independently. This control approach is particularly suitable for motion systems, such as machine tools, which have more drives or actuators than degrees of freedom of movement. This paper deals with the pre-investigation of the modal-based vibration control for machine tools with additional actuators. The object of investigation is an elastic system with a movable saddle. The modal-based control is compared with a local control approach. The results obtained experimentally on the test rig are presented. The modal control is superior since, with the modal approach, each control loop corresponds to a specific vibration mode, and the control law for this loop is designed to provide the desired performance of the control system at the corresponding resonance frequency. The parameterisation of the control loops is simplified by modal control, since the modes can be controlled independently.

6

Effects of variation in measurement chain on temperature measurement calibration with resistant temperature sensors

Deutsch Jessica, Riedel Mirko, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2019

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Vol. 19, No. 3

56--65

EN

Temperature is one of the most important key parameter to consider in measurement and mechanical engineering, because every measurement has to be conducted with reference to standard temperature conditions (20°C, ISO 1). Strictly speaking, almost every measurement depends on the accuracy of the temperature measurement, which requires proper calibration. Therefore, standards list detailed criteria to fulfil temperature calibration with high precision. In fact, any calibration is only valid, if the whole measurement chain is taken into account. This would make recalibration necessary with each variation of the components in the measuring set-up (varying cable length, different measurement channel etc.), which is time-consuming or even impossible in practice. For that reason, this paper presents a practicable calibration strategy, which specifies each component individually and later combines the calibration results according to the composition of the measurement chain. This provides a fast and useful way to achieve the required accuracy of temperature measurement. The examined, exemplary measurement chain consists of an industrial platinum resistance thermometer (IPRT), cables with different lengths, an electrical amplifier and a reference temperature calibrator.

7

Design approach for high-dynamic planar motion systems based on the principle of Kinematically Coupled Force Compensation

Ihlenfeldt Steffen, Müller Jens, Merx Marcel, Peukert Christoph

Journal of Machine Engineering

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2019

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Vol. 19, No. 2

5--17

EN

Machine tools’ feed dynamics are usually limited in order to reduce excitation of machine structure oscillations. Consequently, the potential increase in productivity provided by direct drives, e.g. linear motors, cannot be exploited. The novel approach of the Kinematically Coupled Force Compensation (KCFC) applies a redundant axis configuration combined with the principle of force compensation and thus achieves an increase in feed dynamics while drive reaction forces cancel out each other in the machine base. In this paper, the principle of KCFC is introduced briefly. Subsequently, the basics for the realisation of a highly dynamic KCFC motion system with planar motion are derived and discussed. In order to achieve highest acceleration (> 100 m/s2) and jerk (> 100000 m/s3), a mechatronic system with specially designed components for the mechanical, electrical and control system is required. Thus, the design approach presented in this paper applies lightweight slides, a decoupled guide frame and voice coil motors operated at high frequencies for the pulse width modulation and control loops.