No abstract

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.

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.

This paper presents the modal control applied to motion systems, in particular for machine tools. This control approach is particularly suitable for over-actuated systems that have more actuators than degrees of freedom. By using the modal approach, the parameterisation of the control loops is simplified since each control loop corresponds to a specific eigenmode. A four-variable modal control of a linear motor-driven gantry system equipped with additional active damping devices is presented to achieve active vibration suppression. This approach is experimentally compared with a conventional control method that does not consider the eigenmodes of the system. The influence of the vibration controllers on the closed position loops is investigated.

Kurzfassung Zur simulativen Untersuchung der Prozess-Maschine-Wechselwirkung bei hochtourig geführten Zerspanprozessen werden Modelle des drehzahlabhängigen Verhaltens des Spindel-Werkzeug-Systems benötigt. Die Identifikation der Parameter sowie die Verifikation dieser Modelle können anhand von Nachgiebigkeitsfrequenzgängen erfolgen, die an der rotierenden Spindel gemessen wurden. Wenn hierbei ein Impulshammer zur Strukturanregung eingesetzt wird, treten auf Grund der Relativbewegung zwischen dem rotierenden Messobjekt und der Kalotte des Impulshammers Reibkräfte in der Kontaktzone auf. Hinsichtlich der Bewertung der gemessenen Frequenzgänge stellt sich dabei die Frage, welche Beträge diese Reibkräfte annehmen können und welchen Einfluss sie auf das Messergebniss ausüben.