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

Abstract

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.

Compliant Joints with Remote Centre of Compliance for the Improvement of the Motion Accuracy of a Gantry Stage

“…Depending on the arrangement of the links, the pivot G can be placed outside of the joint (remote centre). [5] presents a joint configuration, where the pivot is located in its centre. However, the exact centre of the rotation depends on the arrangement of the links, their stiffness matrices as well as the load conditions (see e.g.…”

“…As shown in Section 3.2, this method reduces the rotational stiffness of the joints. In [5], the reduction of the full system's rotational stiffness is shown using measured frequency response functions.…”

“…For this purpose, compliant joints, which consist of a single deformable part, are preferable because of the low friction and backlash [4]. The previous work [5] shows that this strategy improves the bandwidth of the axis. Design of high precision motion systems with compliant elements is often addressed in literature.…”