Master switch for electrically preloaded rack-and-pinion drive systems to increase accuracy

• Applicant: Professor Dr.-Ing. Alexander Verl
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 462185026

The manufacturing quality and dynamics of modern production systems are primarily determined by the drive system used. The most common drive systems are ball screw drives (BSD), rack-and-pinion drives (RPD) and linear direct drives (LDD). The selection depends mainly on the application and the costs. The RPD considered in this project are characterized for use in machine tools (MT) in particular by the fact that their stiffness, in contrast to the established BSD, is independent of the traverse length. LDD also are suitable for use in large MT. Here, however, the high energy requirement as well as the secondary parts, which are required over the entire travel distance, have a negative effect on costs.A central problem of electromechanical drive systems is the backlash in the drive train. The backlash represents a non-linearity and thus influences the control quality of the drive system. In order to meet the requirements of modern production systems, a reduction or compensation of the backlash is necessary. An effective method is electrical preloading. Two drives are used here, which generate different torques so that the respective pinions are preloaded.In addition to the dynamic characteristics of the drive system, high demands are placed on its accuracy. In order to achieve high accuracy, state-of-the-art linear measuring systems are mainly used for direct position control. For direct position control, a measuring system along the entire travel distance is required. This is a central cost factor, especially for MT with large traverse lengths. In order to reduce costs, the measuring system of the drive is often used for indirect position control of large MT. However, this leads to a loss of accuracy.Within the scope of the proposed project, a concept called master switch is to be investigated. This concept intends to improve the accuracy of electrically preloaded RPD with indirect position control so that the indirect controlled system reaches the accuracy range of directly controlled systems. For the first time, the measuring systems of both drives are to be used for position control. The electrical preload ensures that the backlash never occurs within both drivetrains at the same time. This underlies the concept of the master switch: For position control, the measuring system of the drive that is currently not affected by backlash is to be used. It is expected that switching between the measuring systems will already increase the accuracy of electrically preloaded PRD with indirect position control, as the backlash never occurs in the position-controlled subsystem. In order to further increase accuracy and to reach the accuracy of directly controlled systems, an approach to reconstruct the table position using the measuring systems of both drives is to be developed and integrated.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Armin Lechler