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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.

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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.

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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.