Design and Validation of an Experimental Setup for Assessing Transmission Errors in Linear Robotic Axes

Industry 4.0 robotic manufacturing requires increasing levels of accuracy and flexibility to ensure adaptive processes that enhance productivity, quality, and resource efficiency. To extend the workspace of industrial robots, additional linear axes are often introduced. In most cases, these axes employ rack-and-pinion transmissions driven by standard rotary servomechanisms, offering a practical alternative to direct-drive solutions but further degrading the motion accuracy of serial robots, with direct consequences on process quality and reliability. To improve efficiency and reduce process errors and material waste, it is therefore essential to predict and compensate for the transmission errors introduced by such devices. Existing literature describes test rigs for rack-and-pinion drives, typically based on linear encoders. While easy to integrate, such encoders are not widely available in industrial assets, and are less accurate than laser interferometers, which are better suited to high-precision characterization. This thesis presents a novel experimental setup for accurate measurement and analysis of transmission errors in robotic linear axes. The setup was developed in the university laboratory, where a high-payload KUKA robot was mounted on a custom-designed dual-motor linear axis powered by Beckhoff servodrives and controlled via TwinCAT. The design process included the definition of the layout and interferometer integration, dynamic modeling of the axis to estimate motor effort and plan experiments, hardware selection for reliable actuation, experimental matrix design, and synchronization of motor encoder data with interferometer measurements. The setup was validated on a 4 m stroke, demonstrating stable and high-resolution characterization of transmission errors under realistic operating conditions.