Amplitude and Phase Uncertainty Analysis due to Cable Flexing in Robot-Based Measurement Systems

In contrast to classical roll-over-azimuth positioning systems, larger amplitude and phase uncertainties due to cable flexing are to be expected in robot-based measurement ranges. Additional uncertainties arise due to the high flexibility regarding the attainable positions in space and the associated dynamics of the robot. Since the RF cables within the energy supply chain of the robot cannot be mechanically decoupled, they must follow the dynamic movements of the robot arm. For this reason, all mechanically induced effects on amplitude and phase stability are investigated. This includes the RF cables in the energy supply chain of the linear axis and the robot arm as well as the transmission behavior of a two-channel rotary joint. The tested components are terminated using a short and, both, deviations in amplitude and phase, as well as their reproducibility, are determined by reflection measurements. The measurement results prove that the dynamic movements of the robot arm cause the greatest uncertainties. Different measurement sequences are investigated and it is shown that especially complex motion patterns, e.g. circular paths, lead to larger phase deviations of up to ten degrees. Furthermore, possibilities to reduce the uncertainties based on an optimized cable routing or by calibration measurements are discussed.