Kinematic uncertainty analysis of a cable-driven parallel robot based on an error transfer model

Cable-driven parallel robots (CDPRs) are a kind of mechanism with large workspace, fast response, and low inertia. However, due to the existence of fixed pulleys, it is unavoidable to bring uncertain cable lengths and lead to pose errors of the end-effector (EE). The inverse kinematic model of a CDPR for picking up medicines is established by considering radii of fixed pulleys. The influence of radii of fixed pulleys on errors of cable lengths is explored. Error transfer model of the CPDR is constructed, and uncertain sources of cable lengths are analyzed. Based on evidence theory and error transfer model, an evidence theory-based uncertainty analysis method (ETUAM) is presented. The structural performance function for kinematic response is derived based on error transfer model. Belief and plausibility measures of joint focal elements under the given threshold are obtained. Kinematic error simulations show that errors of cable lengths become larger with the increase of radii of fixed pulleys. Compared with the vertex method and Monte Carlo method, numerical examples demonstrate the accuracy and efficiency of the ETUAM when it comes to the kinematic uncertainty analysis of the CDPR.

Coupling and Decoupling Measurement Method of Complete Geometric Errors for Multi-Axis Machine Tools

Precision and ultra-precision machining technology rely mainly on the machine tools’ accuracy. To improve it, the measurement, calculation, prediction and control of geometric errors are critical. The traditional measurement methods have lower precision because of ignoring small angle errors. To obtain complete geometric errors of multi-axis machine tools, this paper proposes a new method of coupling and decoupling measurement. Specifically, we used a laser interferometer and dial indicators to measure 36 items of complete geometric errors of multi-axis machine tools. A homogeneous transformation matrix (HTM) was applied to model the error transfer route. The transfer law of complete errors for each machining point was explored and derived. Furthermore, we selected and calculated integrated errors of 36 machining points. Finally, we proved the correctness of the method by comparing the measurement result of a ball bar test and coupling and decoupling measurement of geometric errors. We found that items of small geometric angle errors have a greater impact on machining accuracy than those of geometric displacement errors. Complete geometric errors measured via the coupling and decoupling measurement method can evaluate integrated errors more precisely and comprehensively.

Research on Target Searching Strategy Using Mutual Cueing of Multi-sensor in Multi-platform

The cueing model for sensor cueing phased array radar is built in this paper to research the mutual cueing of multi-sensor in multi-platform for target searching. For the purpose of establishing the distribution probability density model of targets in cueing airspace, cueing error of multi-platform is derived with error transfer method. The successful cueing probability and false hand-off probability between platforms are analyzed, meanwhile the requirement of timeliness is defined. An optimized target searching strategy of cueing radar which adopts distance search through using the cueing center as starting point and controlling false hand-off probability of a single wave position is put forward. The simulation result illustrates that the searching strategy can significantly save radar search resources to capture target successfully, simultaneously decrease the false hand-off probability. The strategy can be applied to the design of dynamic programming software of multi-sensor in multi-platform for collaborative search, which requires accuracy and real-time capability.